The atria receive blood coming back to the heart. The ventricles pump the blood out of the heart. Blood vessels, which compose a network of arteries, and veins that carry blood throughout the body.
Arteries transport blood from the heart to the body tissues.
Veins carry blood back to the heart. Four valves to prevent backward flow of blood. Each valve has flaps, called leaflets, that allow the forward flow of blood and prevent the backward flow. An electrical system of the heart controls how fast it beats. The heart is the hardest working muscle in the human body.