The human heart works as a pump that circulates blood throughout the body. Roughly the size of an adult's clenched fist, it consists of four chambers and conducts the blood through veins and arteries. The septum, or inner wall of the heart, allows each half of the heart muscle to perform its function without interference from the other.
The four chambers of the heart are the right and left atria and the right and left ventricles. The atria, located in the upper portion of the heart, are responsible for collecting blood as it flows into the heart muscle. The ventricles are the two bottom-most chambers and conduct the blood out of the heart to the lungs and the rest of the body.
Arteries are the main blood vessels that carry blood away from the heart. The two most important arteries are the aorta and pulmonary artery. The aorta carries blood to the body from the heart's left side, and the pulmonary artery carries it to the lungs. Veins carry blood to the heart for circulation to the rest of the body, particularly after being oxygenated by the lungs. Scientists estimate that a healthy human heart beats upwards of 100,000 times each day.