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The aortic valve

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© Dr Richard Wellings, Warwick Medical School, West Midlands Surgical Training Centre, UHCW Trust, 2013

In an experiment that reprised his investigation of the brain a few years earlier, Leonardo injected molten wax into the left ventricle and aorta of an ox’s heart, to determine the shape of the sinus (widening) at the root of the aorta, just beyond the aortic valve. He then made a glass model of the sinus, shown in cross-section at top right, and pumped water mixed with grass seeds through the model.

Leonardo observed swirling eddies within the sinus of his model, and concluded that such eddies were crucial in closing the aortic valve when blood flow ceased after each beat of the heart. This brilliant observation was confirmed by medical science only in recent years.

The aortic valve, RCIN 919082 ©

Above is a false-colour MRI scan of a beating heart, obtained using a 10-tonne magnet 30,000 times stronger than the earth’s magnetic field. The left ventricle is seen pumping blood through the aortic valve into the aorta. After each beat of the heart, swirling eddies of blood can be made out in the sinus, exactly as Leonardo postulated (left).

In twenty drawings and notes running to over 1500 words, Leonardo describes in minute detail the eddies of blood that help to close the aortic valve. He had an almost perfect understanding of the action of the valves and the motion of the heart. The discovery of the circulation of the blood was within his grasp.

But Leonardo could not free himself from the belief that the heart simply pumped blood out and then sucked it back. Unable to reconcile what he observed with what he believed to be true Leonardo’s anatomical work came to an end.