<P> Coronary artery bypass surgery is one such operation . In this operation, one or more arteries surrounding the heart that have become narrowed are bypassed . This is done by taking blood vessels harvested from another part of the body . Commonly harvested veins include the saphenous veins or the internal mammary artery . Because this operation involves the heart tissue, a machine is used so that blood can bypass the heart during the operation . </P> <P> Heart valve repair or valve replacement are options for diseases of the heart valves . </P> <P> Humans have known about the heart since ancient times, although its precise function and anatomy were not clearly understood . From the primarily religious views of earlier societies towards the heart, ancient Greeks are considered to have been the primary seat of scientific understanding of the heart in the ancient world . Aristotle considered the heart to be organ responsible for creating blood; Plato considered the heart as the source of circulating blood and Hippocrates noted blood circulating cyclically from the body through the heart to the lungs . Erasistratos (304--250 BCE) noted the heart as a pump, causing dilation of blood vessels, and noted that arteries and veins both radiate from the heart, becoming progressively smaller with distance, although he believed they were filled with air and not blood . He also discovered the heart valves . </P> <P> The Greek physician Galen (2nd century CE) knew blood vessels carried blood and identified venous (dark red) and arterial (brighter and thinner) blood, each with distinct and separate functions . Galen, noting the heart as the hottest organ in the body, concluded that it provided heat to the body . The heart did not pump blood around, the heart's motion sucked blood in during diastole and the blood moved by the pulsation of the arteries themselves . Galen believed the arterial blood was created by venous blood passing from the left ventricle to the right through' pores' between the ventricles . Air from the lungs passed from the lungs via the pulmonary artery to the left side of the heart and created arterial blood . </P>

Who discovered the different valves of the heart