What is the size of a giraffe’s heart?
“Giraffe have this huge problem of having a head that is 2m away from the heart. So in a really big animal how does it get blood up there?” (Professor 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. Additionally, the heart beats up to 170 times per minute double that of humans. 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.
(Ref: image from Channel 4 “Inside Giant Animals – The Giraffe”.)
Cross section of the giraffe”s heart
the left ventricle showing the right ventricle showing the
the very thick muscle wall much smaller muscle wall
The right ventricle pumps the blood the short distance to the lungs and the muscle is about 1cm 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 15cm increase in the length of the neck the left ventricle wall gets another ½ cm thicker.