[Sax. heort.] A hollow muscular organ, with four chambers, in the higher animals. It is the centre of the blood's motion in an animal body, and is situated in the thorax. The blood flows from the veins to the two right chambers of the heart (auricle and ventricle), then to the lungs, next to the two left chambers, from which it is driven into the arteries. Thus the circulation is carried on and life maintained. The heart of a reptile has only three chambers, and of a fish only two, so that the blood is imperfectly aerated, and there is little animal heat.