Sleepy Heartbeat

The single most important sound that you will ever make is the one that you seem to always forget, thumping loyally away in your very chest. The ever present beat of your heart is able to slow down for a slight rest when you take your daily nap on the sofa, snoring away your worries, letting your organs let go of a little stress at the same time. It's a healthy thing to take a siesta once in a while. 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 the pulse was a property of arteries themselves. Erasistratos observed the arteries that were cut during life bleed. He ascribed 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 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.