What is the process of the heart pumping?

There are 4 chambers of the heart; 2 atria (upper chambers) and 2 ventricles (lower chambers). Blood flows from the vein into the atrium, and when the pressure of the atrium is higher than the pressure of the ventricle, the valve (tricuspid valve in the right atrium and bicuspid in the left) opens and the blood flows through until the pressure is higher in the ventricle, causing the valve to close. The muscles of the ventricle walls then contract, raising the pressure of the ventricle to increase even more, so the semi-lunar valves open, and blood is pushed up and out of the ventricle and into the artery.