The cardiovascular system is a body system in animals that functions to transport materials to and from cells and also contains white blood cells which help to fight disease. The cardiovascular system delivers nutrients and oxygen to cells and disposes of cellular waste. The human cardiovascular system consists of the heart, blood vessels, veins, arteries, capillaries and blood. Your heart is a muscle that is the centerpiece of the cardiovascular system. It is made up of four chambers called the right and left atrium and the right and left ventricle which are all separated by valves. The aorta is the largest artery in your body and is connected to the heart to pump oxygen rich blood throughout your body. A heart contraction is called a systole. Diastole is the period of time after systole when the heart fills will blood again so that another contraction can pump the blood out of the heart and to the body.