History of discoveries

The valves of the heart were discovered by a physician of the Hippocratean school around the 4th century BC. However, their function was not properly understood then. Because blood pools in the veins after death, arteries look empty. Ancient anatomists assumed they were filled with air and that they were for transport of air.

Philosophers distinguished veins from arteries but thought that the pulse was a property of arteries themselves. Erasistratos observed the arteries that were cut during life bleed. He described the fact to the phenomenon that air escaping from an artery is replaced with blood which entered by very small vessels between veins and arteries. Thus he apparently postulated capillaries but with reversed flow of blood.

The 2nd century AD, Greek physician Galenos (Galen) knew that blood vessels carried blood and identified venous (dark red) and arterial (brighter and thinner) blood, each with distinct and separate functions. Growth and energy were derived from venous blood created in the liver from chyle, while arterial blood gave vitality by containing pneuma (air) and originated in the heart. Blood flowed from both creating organs to all parts of the body where it was consumed and there was no return of blood to the heart or liver. 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 that the arterial blood was created by venous blood passing from the left ventricle to the right through 'pores' in the inter ventricular septum while air passed from the lungs via the pulmonary artery to the left side of the heart. As the arterial blood was created, 'sooty' vapors were created and passed to the lungs, also via the pulmonary artery, to be exhaled.

The first major scientific understanding of the heart was put forth by the medieval Arab polymath Ibn Al-Nafis, regarded as the father of circulatory physiology.^[12] He was the first physician to correctly describe pulmonary circulation,^[13] the capillary^[14] and coronary circulations.^[15] Prior to this, Galen's theory was widely accepted, and improved upon by Avicenna. Al-Nafis rejected the Galen-Avicenna theory and corrected many wrong ideas that were put forth by it, and also adding his new found observations of pulse and circulation to the new theory. His major observations include (as surmised by Dr. Paul Ghalioungui):^[14]

1. "Denying the existence of any pores through the interventricular septum."
2. "The flow of blood from the right ventricle to the lungs where its lighter parts filter into the pulmonary vein to mix with air."
3. "The notion that blood, or spirit from the mixture of blood and air, passes from the lung to the left ventricle, and not in the opposite direction."
4. "The assertion that there are only two ventricles, not three as stated by Avicenna."
5. "The statement that the ventricle takes its nourishment from blood flowing in the vessels that run in its substance (i.e. the coronary vessels) and not, as Avicenna maintained, from blood deposited in the right ventricle."
6. "A premonition of the capillary circulation in his assertion that the pulmonary vein receives what comes out of the pulmonary artery, this being the reason for the existence of perceptible passages between the two."

Ibn Al-Nafis also corrected Galen-Avicenna assertion that heart has a bone structure through his own observations and wrote the following criticism on it:^[16]

"This is not true. There are absolutely no bones beneath the heart as it is positioned right in the middle of the chest cavity where there are no bones a

A preserved human heart