The heart is the pump of the human circulatory or cardiovascular system. This four-chamber organ pumps the blood that transports cells throughout the body, providing oxygen and nutrients, removing CO2 and waste, and distributing hormones.
There are two sides to the heart. The right side pumps blood through the lungs, and the left side pumps blood throughout the body.
Deoxygenated blood carrying CO2 enters the upper right chamber of the heart known as the right atrium. It passes down a one-way valve into the right ventricle. The ventricles are thick, muscular-walled chambers that pump blood out of the heart. When the heart beats, it squeezes the blood in the right ventricle through the pulmonary artery, another one-way valve, toward the lungs. The blood passes through the lungs, where it exchanges carbon dioxide for oxygen. Oxygenated blood flows out of the lungs and into the upper left atrium. From there it passes through a one-way valve into the lower left chamber of the heart, the left ventricle. When the heart beats, it squeezes the blood in the left ventricle and pumps it into the aorta.
A normal resting heart rate for adults ranges from 60 to 100 beats per minute. The heart rate is controlled by pacemaker cells in the sinoatrial (SA) node. These cells spontaneously depolarize, creating an electrical current that stimulates the right and left atrium. This signal passes to the atrioventricular (AV) node where it is delayed slightly before traveling to the left and right ventricle. This delay enables the atrial contractions to fill the ventricles prior to ventricular contraction, improving pumping effectiveness. Cardiac output is a measure of the performance of the heart. It is the product of the heart rate and stroke volume (CO = HR x SV).
