The human heart is one of the hardest-working organs in the body.
On average, it beats around 75 times a minute. As the heart beats, it provides pressure so blood can flow to deliver oxygen and important nutrients to tissue all over your body through an extensive network of arteries, and it has return blood flow through a network of veins.
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 sternum and ribcage, and between your two lungs.
The heart’s chambers
The heart’s four chambers function as a double-sided pump, with an upper and continuous lower chamber on each side of the heart.
The heart’s four chambers are:
- Right atrium. This chamber receives venous oxygen-depleted blood that has already circulated around through the body, not including the lungs, 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 in exchange for carbon dioxide.
- Left atrium. This chamber receives oxygenated blood from the pulmonary veins of the lungs and pumps it to the left ventricle.
- Left ventricle. With the thickest muscle mass of all the chambers, the left ventricle is the hardest pumping part of the heart, as it pumps blood that flows to the heart and rest of the body other than the lungs.
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 chambers fill 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, also called the sinoatrial node (SA node), located in the tissue of your right atrium.
The pulses then travel through your heart to the atrioventricular node, also called the 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’s valves
The heart has four valves, one each at the downstream end of each chamber, so that, under normal conditions, blood can’t flow backward, and the chambers can fill with blood and pump blood forward properly. These valves can sometimes be repaired or 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 left ventricle into the pulmonary artery to the lungs, so that the heart and rest of the body 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 left ventricle so that the blood can flow to the heart and the rest of body, save the lungs.
Blood flow through
When working properly, deoxygenated blood coming back from organs, other than the lungs, enters the heart through two major veins known as the vena cavae, and the heart returns its venous blood back to itself through the coronary sinus.
From these venous structures, 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 artery trunk, and next travels through the right and left pulmonary arteries to the lungs, where the blood receives oxygen during air exchange.
On its way back from the lungs, the oxygenated blood travels through the right and left pulmonary veins into the left atrium of the heart. The blood then flows through the mitral valve into the left ventricle, the heart’s powerhouse chamber.
The blood travels out the left ventricle through the aortic valve, and into the aorta, extending upward from the heart. From there, the blood moves through a maze of arteries to get to every cell in the body other than the lungs.
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, also called coronary artery disease, typically develops when calcium containing cholesterol and fat plaques collect in and hurt the arteries that feed the heart muscle. If a portion of one of these plaques ruptures, it can suddenly block one of the vessels and cause the heart muscle to begin to die (myocardial infarction) because it’s starved for oxygen and nutrients. This can also occur if a blood clot forms in one of the arteries of the heart, which can happen right after a plaque rupture.