This muscular, roughly cone-shaped organ pumps blood throughout the body. Lying behind the sternum between the lungs, it is about the size of a closed fist and weights between 225-275 grams in females and about 275 - 345 grams in males. The heat is divided into left and right sides by a septum; each sides has and upper atrium and lower ventricle. Through coordinated nerve impulses and muscular contractions , initiated in the the sinoatrial node of the right atrium, the heart pumps blood throughout the body. The heard normally beats about 70 times per minute and it it is nourished by coronary blood vessels. The video shows in graphic detail some of the issues that arise when the electrical impulses go awry. Click on the button below for more detailed information.