The cardiovascular system circulates blood throughout the body using the heart and blood vessels. It has two circuits: pulmonary circulation between the heart and lungs, and systemic circulation carrying oxygenated blood to tissues. The heart has four chambers that pump blood into the arteries, which branch into capillaries and veins to return blood to the heart. Common procedures for heart issues include thrombolytic therapy using drugs to dissolve blood clots, cardiac CT scans using x-rays to image the heart, and stress tests examining heart function during exercise.