The cardiovascular system functions to generate blood pressure, route blood through separate pulmonary and systemic circulations, and ensure one-way blood flow through heart valves. The heart regulates blood supply by matching contraction rate and force to metabolic needs, and can increase cardiac output up to 500%. The heart has four chambers - two atria that receive blood and two ventricles that pump blood to the lungs and body. Deoxygenated blood enters the right atrium while oxygenated blood enters the left atrium, and the ventricles then pump blood to the lungs and aorta. The heart contracts as a unit through its conduction system including the sinoatrial node, atrial and ventricular syncytia, and coordinated chamber contraction and relaxation