The human heart is one of the hardest-working organs in the body. On average, it beats 72 times a minute. As the heart beats, it provides pressure so blood can deliver oxygen and important nutrients to tissue all over your body through an extensive network of arteries. In fact, the heart steadily pumps an average of 2,000 gallons of blood through the body each day.

Your heart is located underneath your ribs, and between your two lungs.

The Heart’s Parts

The heart’s four chambers function as a double-sided pump. The right side of the heart takes in oxygen-depleted blood from the organs. This blood is delivered to the heart through the veins. The chambers on the left side pump oxygen-rich blood out to the body through arteries.

The heart’s four chambers are:

  • Right atrium: This chamber receives oxygen-depleted blood that has already circulated around the body and pumps it into the right ventricle.
  • Right ventricle: The right ventricle pumps blood from the right atrium to the pulmonary artery. The pulmonary artery sends the deoxygenated blood to the lungs, where it picks up oxygen.
  • Left atrium: This chamber receives oxygenated blood from the lungs and pumps it to the left ventricle.
  • Left ventricle: The thickest of all the chambers, the left ventricle is the hardest working part of the heart as it pumps blood throughout the whole body.

The heart’s two atria are both located on the top of the heart. They are responsible for receiving blood from your veins.

The heart’s two ventricles are located in the bottom of the heart. They are responsible for pumping blood into your arteries.

Your atria and ventricles contract to make your heart beat and to pump the blood through each chamber. Your heart fills up with blood before each beat, and the contraction pushes the blood out into the next chamber. The contractions are triggered by electrical pulses that start from the sinus node, or sinoatrial node (SA node), located in the wall of your right atrium. The pulses then travel through your heart to the atrioventricular node, or AV node, located near the center of the heart between the atria and the ventricles. These electrical impulses keep your blood flowing in proper rhythm.

The heart has four valves that separate each chamber so that, under normal conditions, blood cannot flow backwards. These valves can sometimes be replaced if they become damaged.

The heart’s valves are:

  • Tricuspid (right AV) valve: This valve opens to allow blood to flow from the right atrium to the right ventricle.
  • Pulmonary valve: This valve opens to allow blood to flow from the heart into the lungs, so that it can receive more oxygen.
  • Mitral (left AV) valve: This valve opens to let blood flow from the left atrium to the left ventricle.
  • Aortic valve: This valve opens to let blood leave the heart and be pumped around the body.

The Heart’s Crown

The structure of the heart’s blood supply is called the coronary circulatory system. The word “coronary” comes from the Latin word meaning “of a crown.” The arteries that fuel the heart’s muscle encircle the heart like a crown.

Coronary heart disease develops when cholesterol plaques collect in the arteries that feed the heart muscle. If a portion of one of these plaques ruptures, it can block one of the vessels and cause the heart muscle to begin to die because it is starved for oxygen and nutrients. This can also occur if a blood clot forms in one of the arteries of the heart.

Blood Flow Through the Heart

When working properly, deoxygenated blood coming back from organs enters the heart through two major veins known as the vena cavae. From there, the blood enters the right atrium and passes through the tricuspid valve into the right ventricle. The blood then flows through the pulmonary valve into the pulmonary trunk, and then travels through one of two pulmonary arteries out to the lungs where it receives oxygen.

On its way back from the lungs, the blood travels through four pulmonary veins into the left atrium at the top of the heart. The blood then flows through the mitral valve into the left ventricle, the heart’s powerhouse. The blood quickly travels out the left ventricle through the aortic valve, and into the ascending aorta, a portion of the aorta artery extending upward from the heart. From there, the blood travels through a maze of arteries to get to every cell in the body.