Heart

The exterior of a healthy heart, showing the front surface of heart, including the coronary arteries and major blood vessels. Source: NHLBI.

The heart is a pump for blood. It is the hub of the body's cardiovascular system.

Long recognized for its vital importance to life, the heart also has metaphorical associations. It is thought of as the essential or most vital part of something and the key to one's innermost character, feelings, or inclinations.^[1]

Cross-section of a healthy heart. The blue arrow shows the direction in which low-oxygen blood flows from the body to the lungs. The red arrow shows the direction in which oxygen-rich blood flows from the lungs to the rest of the body. Source: NHLBI.

Description

The heart is located under the ribcage in the center of the chest between the right and left lung. It is shaped like an upside-down pear. Its muscular walls beat, or contract, pumping blood continuously to all parts of the body.

The size of the heart can vary depending on age, size, and the condition of the heart. A normal, healthy, adult heart most often is the size of an average clenched adult fist. Some diseases of the heart can cause it to become larger.

Exterior

The heart is composed of muscle. Connected to the heart are some of the main blood vessels (arteries and veins) that make up the circulatory system.

Blood is pumped from the right side of the heart to the lungs. When air is inhaled, oxygen passes from the lungs through tiny blood vessels, where it is added to the blood. Carbon dioxide, a waste product, is passed in the opposite direction, from the blood through these vessels back into the lungs. It is then removed from the body when air is exhaled.

The left side of the heart receives oxygen-rich blood from the lungs. This oxygen-rich blood is then sent from the left side of the heart through the aorta (a main artery) to the rest of the body.

The right side of the heart

The superior and inferior venae cavae are the largest veins in the body. They carry used (oxygen-poor) blood to the right atrium of the heart. Used blood has had its oxygen removed and used by the body's organs and tissues. The superior vena cava carries used blood from the upper parts of the body, including the head, chest, arms, and neck. The inferior vena cava carries used blood from the lower parts of the body.

The used blood from the venae cavae flows into the heart's right atrium and then on to the right ventricle (see the heart chambers discussion below for a description of the atria and ventricles). From the right ventricle, the used blood is pumped through the pulmonary arteries to the lungs. Here, through many small, thin blood vessels called capillaries, the blood picks up oxygen needed by all the areas of the body.

The oxygen-rich blood passes from the lungs back to the heart through the pulmonary veins.

The left side of the heart

Oxygen-rich blood from the lungs passes through the pulmonary veins. It enters the left atrium and is pumped into the left ventricle. From the left ventricle, blood is pumped to the rest of the body through the aorta.

Like all organs, the heart needs blood rich with oxygen. This oxygen is supplied by the blood in the coronary arteries as it is pumped out of the heart's left ventricle. The coronary arteries are located on the heart's surface at the beginning of the aorta. The coronary arteries carry oxygen-rich blood to all parts of the heart.

Interior

Heart chambers

The heart has four chambers. The two upper chambers are called atria. The atria receive and collect blood. The two lower chambers are called ventricles. The ventricles pump blood out of the heart into the circulatory system to other parts of the body.

The septum

The right and left sides of the heart are divided by an internal wall of tissue called the septum. The area of the septum that divides the two upper chambers (atria) of the heart is called the atrial or interatrial septum. The area of the septum that divides the two lower chambers (ventricles) of the heart is called the ventricular or interventricular septum.

Heart valves

The heart contains four valves that function to maintain unidirectional blood flow across the ventricles. The atrioventricular (AV) valves prevent blood from flowing backwards into the atria and are known as the mitral valve (on the left) and the tricuspid valve (on the right). The other two valves lie between the ventricles and the great arteries: the aortic valve separates the left ventricle from the aorta, and the pulmonary valve separates the right ventricle from the pulmonary artery. Heart valves occasionally lose their ability to prevent retrograde flow (a condition known as regurgitation or incompetence) or may not open enough to allow unrestricted flow (a condition known as stenosis). Diseased valves may be surgically repaired or replaced with manufactured valves or valves taken from humans, cows, or pigs.

Blood flow

Blood enters the right atrium of the heart from the superior and inferior vena cavae. From the right atrium, blood is pumped into the right ventricle. From the right ventricle, blood is pumped to the lungs through the pulmonary arteries.

Oxygen-rich blood coming in from the lungs through the pulmonary veins enters into the left atrium. From the left atrium, the blood is pumped into the left ventricle, where it is pumped to the rest of the body through the aorta.

For the heart to function properly, blood flows in only one direction. The heart's valves make this possible. Both of the ventricles has an in (inlet) valve from the atria and an out (outlet) valve leading to the arteries. Healthy valves open and close in very exact coordination with the pumping action of the atria and ventricles. Each valve has a set of flaps called leaflets or cusps, which seal or open the valves. This allows pumped blood to keep flowing forward through the chambers and into the arteries without backing up.

Role of the Heart in the Body

The heart is vital to health and nearly everything that goes on in the body. Without the heart's pumping action, blood can't circulate within the body. A healthy heart supplies the body with the right amount of blood at the right rate needed to function normally.

How It Works

The heart is a muscular organ that acts like a pump to send blood throughout the body continuously. The heart is at the center of the circulatory system, which delivers (circulates) blood to all areas of the body. An electrical system regulates the heart and uses electrical signals to contract the heart muscle (called myocardium). When the walls contract, blood is pumped into the circulatory system.

The circulatory system is made up of a network of blood vessels, such as arteries, veins, and capillaries. The vessels in this network carry blood to and from all areas of the body. A system of inlet and outlet valves in the heart's chambers works to ensure that blood flows in the right direction.

Blood carries the oxygen and nutrients that organs need to function normally. Blood also carries carbon dioxide, a waste product, to the lungs to be passed out of the body and into the air.

Contraction

Heartbeat

When the heart beats, it makes a "lub-DUB" sound. Between the "lub" and the "DUB," blood is pumped through the heart and circulatory system.

A heartbeat may seem like a simple event repeated over and over. A heartbeat actually is a complicated series of very precise and coordinated events that take place inside and around the heart. Each side of the heart uses an inlet valve to help move blood between the atrium and ventricle. The tricuspid valve does this between the right atrium and right ventricle. The mitral valve does this between the left atrium and left ventricle. The "lub" is the sound of the mitral and tricuspid valves closing.

Each of the heart's ventricles has an outlet valve. The right ventricle uses the pulmonary valve to help move blood into the pulmonary arteries. The left ventricle uses the aortic valve to do the same for the aorta. The "DUB" is the sound of the aortic and pulmonary valves closing.

Each heartbeat has two basic parts: diastole (relaxation) and atrial and ventricular systole (contraction). During diastole, the atria and ventricles relax and begin to fill with blood. At the end of diastole, the atria contract (an event called atrial systole) and pump blood into the ventricles. The atria then begin to relax. Next, the ventricles contract (an event called ventricular systole) and pump blood out of the heart.

Pumping action

The four valves ensure the blood flows only in one direction. Healthy valves open and close in coordination with the pumping action of the atria and ventricles. Each valve has a set of flaps called leaflets or cusps. These seal or open the valves. This allows pumped blood to pass through the chambers and into the blood vessels without backing up.

Blood without oxygen flows from the two venae cavae and fills the right atrium. The atrium contracts (atrial systole). The tricuspid valve located between the right atrium and right ventricle opens for a short time and then shuts. This allows blood to enter into the right ventricle without flowing back into the right atrium.

When the right ventricle fills with blood, it contracts (ventricular systole). The pulmonary valve located between the right ventricle and pulmonary artery opens and closes quickly. This allows blood to enter into the pulmonary artery without flowing back into the right ventricle. This is important because the right ventricle begins to refill with more blood through the tricuspid valve during this time. Blood then travels through the pulmonary arteries to the lungs to pick up oxygen.

Oxygen-rich blood returns from the lungs to the left atrium through the pulmonary veins. As the left atrium fills with blood, it contracts. This event also is called atrial systole. The mitral valve located between the left atrium and left ventricle opens and closes quickly. This allows blood to pass from the left atrium into the left ventricle without flowing back into the left atrium.

As the left ventricle fills with blood, it contracts. This event also is called ventricular systole. The aortic valve located between the left ventricle and aorta opens and allows blood to flow into the aorta. The aorta is the main artery that carries blood from the heart to the rest of the body. The aortic valve closes quickly to prevent blood from flowing back into the left ventricle, which is already filling up with freshly-oxygenated blood.

Circulation

The heart and blood vessels make up the overall blood circulatory system. The overall blood circulatory system is made up of the following four subsystems:

Arterial circulation

Arterial circulation is the part of the overall blood circulatory system that involves arteries, like the aorta and pulmonary arteries.

Arteries are blood vessels that carry oxygenated blood away from the heart. Healthy arteries are strong and elastic. They become more narrow between beats of the heart, which helps to keep the blood pressure consistent. This helps blood circulate efficiently through the body.

Arteries branch into smaller blood vessels called arterioles. Arteries and arterioles have strong, flexible walls that allow them to adjust to the amount and rate of blood flowing to different parts of the body.

Venous circulation

Venous circulation is the part of the overall blood circulatory system that involves veins, like the venae cavae and pulmonary veins. Veins are blood vessels that carry blood back to the heart. Veins have thinner walls than arteries. Veins can increase in width as the amount of blood passing through them increases.

Capillary circulation

Capillary circulation is the part of the circulatory system where oxygen, nutrients, and waste pass between the blood and parts of the body.

Capillaries connect the arterial and venous circulatory subsystems. Capillaries are very small blood vessels.

The importance of capillaries lies in their very thin walls. Unlike arteries and veins, capillary walls are thin enough that oxygen and nutrients in the blood can pass through the walls to the parts of the body that need them to function normally. Capillaries' thin walls also allow waste products like carbon dioxide to pass from the body's organs and tissues into the blood, where it's taken away to the lungs.

Pulmonary circulation

Pulmonary circulation is the movement of blood from the heart to the lungs and back to the heart again. Pulmonary circulation includes both arterial and venous circulation.

Blood without oxygen is pumped to the lungs from the heart (arterial circulation). Oxygen-rich blood moves from the lungs to the heart through the pulmonary veins (venous circulation).

Pulmonary circulation also includes capillary circulation. Inhaled oxygen passes through the lungs into the blood through the many capillaries in the lungs. Oxygen-rich blood moves through the pulmonary veins to the left side of the heart and out the aorta to the rest of the body. Capillaries in the lungs also remove carbon dioxide from the blood so that the lungs can release the carbon dioxide out into the air as a person breathes.

Electrical system

Schematic of an electrocardiogram. Source: Wikimedia Commons.

The heart’s electrical system controls all the events that occur when it pumps blood. The electrical system is also called the cardiac conduction system. An EKG (electrocardiogram) is a graphical picture of the electrical activity of the heart.

The heart’s electrical system is made up of three main parts.

• The sinoatrial (SA) node, located in the right atrium
• The atrioventricular (AV) node, located on the interatrial septum close to the tricuspid valve
• The His-Purkinje system, located along the walls of the ventricles

A heartbeat is a single cycle in which the heart’s chambers relax and contract to pump blood. This cycle includes the opening and closing of the two inlet and outlet valves of the right and left ventricles of the heart.

Each heartbeat has two basic parts: diastole, and atrial and ventricular systole. During diastole, the atria and ventricles of the heart relax and begin to fill with blood. At the end of diastole, the heart’s atria contract (atrial systole), pumping blood into the ventricles, and then begin to relax. The heart’s ventricles then contract (ventricular systole), pumping blood out of the heart.

Each beat of the heart is set in motion by an electrical signal from within the heart muscle. In a normal, healthy heart, each beat begins with a signal from the SA node. This is why the SA node is sometimes called the heart’s natural pacemaker. The pulse, or heart rate, is the number of signals the SA node produces per minute.

The signal is generated as the two venae cavae fill the right atrium with blood from other parts of the body. The signal spreads across the cells of the right and left atria. This signal causes the atria to contract. This action pushes blood through the open valves from the atria into both ventricles.

The signal arrives at the AV node near the ventricles, where it slows for an instant to allow the heart’s right and left ventricles to fill with blood. The signal is released and moves to the His bundle located in the walls of the ventricles.

From the His bundle, the signal fibers divide into left and right bundle branches through the Purkinje fibers that connect directly to the cells in the walls of the heart’s left and right ventricles. As the electrical signal spreads across the cells of the heart’s ventricle walls, both ventricles contract, but not at exactly the same moment. The left ventricle contracts an instant before the right ventricle. This pushes blood through the pulmonary valve (for the right ventricle) to the lungs, and through the aortic valve (for the left ventricle) to the rest of the body.

As the signal passes, the walls of the ventricles relax and await the next signal.

This process continues over and over as the atria refill with blood and other electrical signals come from the SA node.

Diseases of the Heart

If disease or injury weakens the heart, the body's organs won't receive enough oxygenated blood to function normally. Heart disease can disrupt a heart's normal electrical system and pumping functions. Diseases and conditions of the heart's muscle make it difficult for the heart to pump blood normally. Damaged or diseased blood vessels make the heart work harder than normal. Problems with the heart's electrical system, called arrhythmias, can make it difficult for the heart to pump blood efficiently.

Diseases of the heart include the following:

• Arrhythmias, such as:
  • Atrial Fibrillation
• Atrial septal defect
• Cardiomyopathy
• Congenital heart disease, such as:
  • Patent ductus arteriosus
  • Tetralogy of Fallot
• Coronary artery disease
• Coronary microvascular disease
• Heart attack
• Heart block
• Heart failure
• Heart murmur
• Mitral valve prolapse
• Pericarditis
• Cardiac arrest
• Ventricular septal defect

Symptoms

Symptoms of a heart problem include the following:

• Angina pectoris
• Palpitations

Related conditions

Conditions that may affect the heart include the following:

• Atherosclerosis
• High Blood Cholesterol
• High blood pressure
• Hypotension
• Kawasaki disease
• Long QT syndrome
• Marfan syndrome
• Metabolic syndrome
• Obesity

Procedures

Some procedures performed to diagnose or treat heart disease are listed here:

• Cardiac catheterization
• Cardiac rehabilitation
• Catheter ablation
• Angioplasty
• Cardiac Stents
• Stress Testing

Surgery

• Coronary artery bypass grafting
• Defibrillator placement
• Heart surgery
• Heart transplant
• Pacemaker placement

Open Heart Surgery (Sentara Cardiac Patient Education)


Heart Catheterization (Sentara Cardiac Patient Education)

Radiographic studies

• Cardiac CT
• Cardiac MRI
• Coronary angiography
• Coronary calcium scan
• Echocardiography
• Electrocardiogram (EKG/ECG)
• Holter and event monitors
• Nuclear heart scan

History

Milestones

1628— William Harvey, an English Physician, first describes the circulation of the blood.

1706— Raymond Vieussens, a French anatomy professor, first describes the structure of the heart's chambers and vessels.

1733— Stephen Hales, an English clergyman and scientist, first measures blood pressure.

1816— Rene Laennec, a French physician, invents the stethoscope.

1903— Willem Einthoven, a Dutch physiologist, develops the electrocardiograph.

1912— James Herrick, an American physician, first describes heart disease resulting from hardening of the arteries.

1938— Robert E. Gross, an American surgeon, performs first heart surgery.

1952—F. John Lewis, an American surgeon, performs first successful open heart surgery.^[2]

1961—J. R. Jude, an American cardiologist, leads a team performing the first external cardiac massage to restart a heart.^[3]

1965— Michael DeBakey and Adrian Kantrowitz, American surgeons, implant mechanical devices to help a diseased heart.

1967— Christiaan Barnard, a South African surgeon, performs the first whole heart transplant from one person to another.

Etymology

Heart comes from Middle English hert and Old English heorte. The term cardiac means related to the heart and comes from the Greek καρδία, kardia. These terms have been in use since before the 12th century.^[1]

Research

Heart disease was relatively unheard of prior to the 20th century. Rates of heart disease rose sharply in the early 1900s. The Framingham Heart Study was developed in 1948 by the National Heart Institute (now known as the National Heart, Lung, and Blood Institute) to identify factors leading to the epidemic of cardiovascular disease. Grandchildren of the original participants in the study are currently being recruited to participate in the Generation III Cohort of the study. Data collected in the Framingham Heart Study has been used to study the effects of cigarette smoking, high cholesterol, high blood pressure, physical activity, obesity, and psychosocial factors on heart disease.^[4]

Recent discoveries

A randomized controlled trial of 464 sedentary women who were postmenopausal and overweight or obese showed that increasing exercise led to improvements in aerobic fitness.^[5]

References

1. ↑ ^{1.0 1.1} Merriam-Webster Online. Heart.
2. ↑ Wikipedia. Open Heart Surgery.
3. ↑ Wikipedia. Cardiopulmonary Resuscitation.
4. ↑ National Heart, Lung, and Blood Institute Web site. Framingham Heart Study
5. ↑ Church TS, Earnest CP, Skinner JS, Blair SN. Effects of different doses of physical activity on cardiorespiratory fitness among sedentary, overweight or obese postmenopausal women with elevated blood pressure: a randomized controlled trial. JAMA. 2007 May 16;297(19):2081-91. Abstract | Full Text

External Links

American Heart Association

National Heart, Lung, and Blood Institute

Nova Online: Electric Heart. The story of the pursuit of an artificial human heart.