Diastolic blood pressure is the main driving pressure for coronary perfusion. Diastolic pressure depends on mean pressure and the ratio of the decay time of aortic pressure in diastole (tau) and the duration of diastole (Td). The ratio of tau, a morphological, arterial parameter, and Td, a functional, cardiac parameter, is the same in all mammals. This could mean that smaller animals have higher heart rates i.e. shorter duration of diastole to match the shorter time constant of the diastolic pressure decay and to guarantee adequate coronary perfusion.