The Heart's Chambers and Valves

The function of the heart is to pump the blood that bathes and nourishes every organ of the body. The blood carries the oxygen and nutrients vital to the tissues, and it also carries waste products away from the tissues. If the pumping action of the heart is disrupted for any reason, the body’s organs begin to fail very quickly. So life itself is dependent on the efficient, continuous operation of the heart.

Heart’s Chambers and Valves

The heart has two “sides.” The right side of the heart accepts “used” blood that is returning from the tissues of the body, and pumps that blood into the lungs, where it is replenished with oxygen. The left side of the heart accepts replenished blood from the lungs, and then pumps that blood out to all the body’s organs.

Each side of the heart has two chambers, for a total of four chambers. The two ventricles (right and left) are muscular chambers capable of propelling the blood out of the heart. The right ventricle pumps blood to the lungs, and the left ventricle pumps blood to all other organs.

The two atria (right and left) accept the blood returning to the heart (from the body’s tissues and from the lungs, respectively). At just the right moment, the right and left atria empty their accumulated blood into the right and left ventricles. 

The four heart valves (tricuspid, pulmonary, mitral and aortic) open and close at just the right moment to keep the blood moving in the proper direction through the heart.

It is helpful to visualize the heart functioning as two separate pumps, working in series; the right heart pump, and the left heart pump. 

The Right Heart Pump

The right heart pump consists of the right atrium, tricuspid valve, right ventricle, pulmonic valve, and pulmonary artery. Its job is to make sure “used” blood gets reloaded with oxygen. Oxygen-poor blood returning to the heart from the body’s tissues enters the right atrium. When the atria contract, the tricuspid valve opens and allows the blood to be pumped from the right atrium to the right ventricle. Then, when the right ventricle contracts, the tricuspid valve closes (to prevent blood from washing backwards into the right atrium), and the pulmonic valve opens — so blood is ejected from the right ventricle and out to the pulmonary artery and the lungs, where it is replenished with oxygen.

• Read about tricuspid regurgitation.
• Read about pulmonary artery hypertension.

The Left Heart Pump

The left heart pump consists of the left atrium, mitral valve, left ventricle, aortic valve, and aorta. Its job is to pump oxygen-rich blood out to the body’s tissues. Blood returning to the heart from the lungs enters the left atrium. When the atria contract, the mitral valve opens and allows the blood to enter the left ventricle. When the left ventricle contracts a moment later, the mitral valve closes and the aortic valve opens. Blood is propelled out of the left ventricle, across the aortic valve, and out to the body.

• Read about mitral stenosis.
• Read about mitral regurgitation.
• Read about aortic stenosis.
• Read about aortic regurgitation.

The Cardiac Cycle

You may hear about a concept called the cardiac cycle. Simply, the “cardiac cycle” is a way doctors have of dividing the work of the heart into two phases — the diastolic phase and the systolic phase. 

During the diastolic phase of the cardiac cycle, the atria are contracting to fill the two ventricles with blood, and the ventricles are “relaxing” in between heart beats. The tricuspid and mitral valves are open during the diastolic phase to allow blood to flow into the ventricles, and the pulmonic and aortic valves are closed to prevent blood from washing backwards into the ventricles. 

During the systolic phase, the two ventricles are contracting to propel blood out to the lungs (right ventricle) and out to the rest of the body (left ventricle). The right atrium is filling with “used” blood from the tissues, and the left atrium is filling with oxygenated blood from the lungs. The tricuspid and mitral valves are closed during systole, and the pulmonic and aortic valves are open.

The concept of the cardiac cycle is useful in several ways. For instance, when we measure blood pressure, we are measuring the pressure in the arteries during both phases of the cardiac cycle — systolic and diastolic. So, blood pressure is reported as two numbers, such as 120/80. Here, the systolic blood pressure (the arterial pressure at the moment the ventricles are beating) is 120 mmHg, and the diastolic pressure (the pressure during ventricular relaxation) is 80 mmHg.

• Read about measuring blood pressure.

Also, when cardiologists talk about heart failure, they often specify whether the cardiac dysfunction primarily affects the systolic portion of cardiac function (as in dilated cardiomyopathy), or the diastolic portion (as in diastolic dysfunction). Proper treatment requires making this distinction. 

Read about the anatomy of the normal coronary arteries.

Finally, it is important to note that the sequence and timing involved in the cardiac cycle — the opening and closing of the four valves and the pumping and relaxing of the four chambers — is critical to normal cardiac function. This timing and sequencing is critically dependent on the cardiac electrical system, which you can read about here.