How big is a giraffe’s heart?

“Giraffe have this huge problem of having a head that is 2 m away from the heart. So in a really big animal how does it get blood up there?” Prof. Graham Mitchell, Centre of Wildlife Studies in Onderstepoort, South Africa

The giraffe has an extremely high blood pressure (280/180 mm Hg), which is twice that found in humans. The heart can beat up to 170 beats per minute when a giraffe is running, but a resting/normal heart rate is around 40-90 beats per minute.

It was previously thought that a giraffe had a really big heart, but recent research has revealed that there isn’t room in the body cavity for this. Instead, the giraffe has a relatively small heart and its power comes from a very strong beat as a result of the incredibly thick walls of the left ventricle.

The right ventricle pumps the blood a short distance to the lungs, and the muscle is about 1 cm thick. The left ventricle has to pump the blood all the way up to the head against the hydrostatic pressure of the blood already in the long vertical artery. A giraffe’s heart has evolved to have thick muscle walls and a small radius giving it great power to overcome this pressure.

The thickness of the muscle wall is related almost directly to the length of the neck. For every 15 cm increase in the length of the neck the left ventricle wall adds another 0.5 cm thickness.

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