How does your heart actually pump blood through your body?

Your heart is a muscular pump divided into four chambers: two atria on top and two ventricles on the bottom. Deoxygenated blood returning from the body enters the right atrium, flows into the right ventricle, and gets pumped to the lungs to pick up oxygen. That freshly oxygenated blood returns to the left atrium, drops into the left ventricle, and then gets forcefully squeezed out through the aorta to circulate through the rest of the body. This squeezing action is called systole, and the relaxation phase that lets chambers refill is called diastole. Electrical signals generated by the sinoatrial node coordinate the timing, triggering the atria to contract first, then the ventricles, creating the rhythmic heartbeat you can feel as your pulse.