The only organ present in the circulatory system is the heart. The blood from the heart goes to the lungs in order to get oxygen. The muscle present in the inner part of the system is the one responsible for the pumping of blood throughout the body when the heart beats. The blood involve in this process is the one that carries the oxygen and nutrients to the rest of the body. It also carries CO2 and waste products. The main role of the heart is to carry oxygen to every cell of the body. It also pumps blood throughout the body helping it to control the heart rate and blood pressure.