The human heart is an organ that pumps blood throughout the body via the circulatory system.
Human heart anatomy
In humans, the heart is roughly the size of a large fist and weighs between 9 and 12 ounces (250 and 350 grams). It has four chambers: two upper chambers (the atria) and two lower ones (the ventricles). The right atrium and right ventricle together make up the "right heart," and the left atrium and left ventricle make up the "left heart." A wall of muscle called the septum separates the two sides of the heart.
A double-walled sac called the pericardium encases the heart, which serves to protect the heart and anchor it inside the chest. Between the outer layer, the parietal pericardium, and the inner layer, the serous pericardium, runs pericardial fluid, which lubricates the heart during contractions and movements of the lungs and diaphragm.
The heart's outer wall consists of three layers. The outermost wall layer, or epicardium, is the inner wall of the pericardium. The middle layer, or myocardium, contains the muscle that contracts. The inner layer, or endocardium, is the lining that contacts the blood.
The tricuspid valve and the mitral valve make up the atrioventricular (AV) valves, which connect the atria and the ventricles. The pulmonary semi-lunar valve separates the left ventricle from the pulmonary artery, and the aortic valve separates the right ventricle from the aorta. The heartstrings, or chordae tendinae, anchor the valves to heart muscles.
The sinoatrial node produces the electrical pulses that drive heart contractions.
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