Well there is this When comparisons of heart rate and life expectancy are adjusted for body weight in mammals it appears that life span is pre determined by the basic energetics of living cells This inverse relationship between heart rate and life expectancy reflects an epiphenomenon in which heart rate is a marker for or a determinant of metabolic rate and energetic needs The metabolic rate is dependent on the physical activity which in turn is related to and likely determined by heart rate itself Regression analysis on a logarithmic scale between body mass and metabolic rate among animals yields a straight line with the same slope as that between body mass and heart rate 19 Therefore there is a close link between temperature metabolism and heart rate and the question is which is the primary control among these parameters If heart rate determines the metabolic rate it follows that a relationship between heart rate and life span exists in the entire animal kingdom including man