Human heart

The human heart is an organ that pumps blood throughout the body via the circulatory system, supplying oxygen and nutrients to the tissues and removing carbon dioxide and other wastes. In humans, the heart weighs between about 280 to 340 grams in men and 230 to 280 grams in women. The human heart has four chambers: two upper chambers (the atria) and two lower ones (the ventricles). A wall of muscle called the septum separates the two sides of the heart. 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.