The human heart pumps blood to all parts of the body. After receiving blood from the body, the heart pumps blood via the lungs to re-oxygenate it. Before pumping it back out to the body.
The heart receives deoxygenated blood from the body in the right atrium and pumps it into the right ventricle. Then it is pumped through to the lungs where it is re-oxygenated. The blood is then received from the lungs in the left atrium and is pumped through to the left ventricle and back out into the body at high pressure. The heart is surrounded by carotid arteries that feed oxygen and nutrients to the heart itself. In the event of a heart attack it is these arteries that get blocked, halting the pumping process as the heart is unable to pump.