Because of its extremely long neck, the giraffe must rely on its oversized heart (two feet long and twenty-five pounds!) to pump blood all the way to its head. As a result, the giraffe has the highest blood pressure of any animal: 280/180 mmHg (millimeters of mercury) at heart level when prone -- more than twice the blood pressure of an average human. Not surprisingly, because of their high blood pressure, giraffes are prone to heart attacks.