The heart is a muscular organ in most animals, which pumps blood through the blood vessels of the circulatory system.Blood provides the body with oxygen and nutrients, as well as assists in the removal of metabolic wastes. In humans, the heart is located between the lungs, in the middle compartment of the chest.In humans, other mammals, and birds, the heart is divided into four chambers: upper left and right atria; and lower left and right ventricles.Commonly the right atrium and ventricle are referred together as the right heart and their left counterparts as the left heart.Fish, in contrast, have two chambers, an atrium and a ventricle, while reptiles have three chambers.source:wikipedia
