HEART, ILLUSTRATION. HEART, ILLUSTRATION The heart is the organ that impels blood circulation. Its muscle, the myocardium, contracts under the effect of nerve impulses, propelling blood through the body. It is composed of 4 chambers : 2 auricles and 2 ventricles For each ventricle there is a corresponding auricle, with a valvular opening between the two for communication. The heart is thus divided into 2 parts, with the blood leaving the right heart, circulating through the lungs and return