Blood is pumped away from the heart through arteries and returns to the heart through veins. The major artery of the body is the aorta and the major veins of the body are the vena cava . The heart is divided by a partition or septum into two halves. The halves are in turn divided into chambers. The upper two chambers of the heart are called atria and the lower two chambers are called ventricles .
Valves allow blood to flow in one direction between the chambers of the heart.
Cardiac muscle cells contract spontaneously and are coordinated by nodal tissue , specifically the sinoatrial node . There are other factors that influence heart rate as well. These include endocrine hormones, body temperature and exercise. Systole - Ventricles contract. Find great deals on quality laboratory equipment.