Most mammals have a relatively low blood pressure because their blood needs only move a short distance between head and heart.For the giraffe the distance is significant.
That creates two problems: a giraffe's heart must cope with the hydrostatic pressure exerted on it by the amount of blood in such a tall neck. For blood to reach the head, the heart must then beat strongly enough to overcome this significant downward pressure caused by gravity.
Previous studies have found the giraffe has an extremely high blood pressure that is twice that found in other animals. But this study is the first to unravel the true nature of the giraffe heart and cardiovascular system.
"For a long time it was thought that the origin of the high blood pressure was a really big heart and that was based on a single measurement based in the 1950s," says Prof Mitchell.
The researchers based their results on a range of measurements taken from giraffes culled in south eastern Zimbabwe between 2006 and 2009.
"Our concern was partly to explain the origin of high blood pressure and what physiological mechanisms operate to push the blood pressure to the level in the giraffe," he says.
"We established that the heart is actually quite small. It's smaller than you'd expect in similar-sized animals, but the walls are incredibly thick," Prof Mitchell says.
"You have a small but a very powerful heart delivering the blood pressure."
The researchers say giraffes are adapted to the high blood pressure and do not suffer as a consequence.
A giraffe's heart has evolved to have thick muscle walls and a small radius, giving it great power.The walls of the blood vessels also thicken with age as the giraffe's neck grows longer, to avoid rupturing under increasing pressure
The giraffe also has other specialist mechanisms to help deal with the high blood pressure, Prof Mitchell says.
"Blood pressure depends on the capacity of the cardiovascular system as well as the efficiency of the pump. Giraffes have got a way of adjusting the capacity of the cardiovascular system and are able to shrink and expand their blood vessels to change the volume of the cardiovascular system very efficiently."
From the data collected on the body dimensions of the dead giraffes, the researchers hope to reveal more about its extraordinary body, including insights into its range of vision and breathing.
Prof Mitchell says it will also be exciting to study the physiology of living giraffes using remote devices to collect data.
"To measure blood pressure in a free living giraffe doing its thing, that would be really interesting," he says.
"For people who study high blood pressure in humans, or people just like me who wonder how giraffes get it right."