Overview of Heart Anatomy and Physiology

The heart is a muscular pump that works continuously to circulate blood through the cardiovascular system. Blood carries oxygen, nutrients, hormones, wastes, and other substances to and from cells of the body. The heart pumps our five liters of blood through the body nearly 1400 times per day, every day of our lives. The human heart is divided into four chambers: two upper chambers, called the atria, and two lower chambers, the ventricles. Near the base of the heart, blood vessels connect to each chamber. Blood enters the heart through the large veins, which empty into the thin-walled atria. Blood leaves the ventricles in large arteries, which carry blood away from the heart. You can think of the heart as two separate pumps operating side-by-side within one organ. A thin interatrial septum separates the two atria, and a thick interventricular septum separates the two ventricles. On the right side, blood enters the right atrium, then travels to the right ventricle. The right ventricle then pumps the blood through the pulmonary circuit and back into the left side of the heart. On the left side, blood enters the left atrium, then travels to the left ventricle. The left ventricle then pumps the blood through the systemic circuit and back into the right side of the heart. When the heart beats, it propels blood simultaneously through these two circuits. In this design, blood flow is unidirectional—that is, it flows in one direction only, first through one circuit, then through the next and back again to the first.