cardiovascular system of the heart, blood vessels, and the approximately 5 liter of blood that the blood vessels transport. Responsible for transporting oxygen, nutrients, hormones, and cellular waste products throughout the body, the cardiovascular system is powered by the body's hardest-working organ - the heart, which is only about the size of closed fist. Even at rest, the average heart easily pumps over 5 liters of blood throughout the body every minute