Rest heart rate and life expectancy.
Among mammals, there is an inverse semilogarithmic relation between heart rate and life expectancy. The product of these variables, namely, the number of heart beats/lifetime, should provide a mathematical expression that defines for each species a predetermined number of heart beats in a lifetime. Plots of the calculated number of heart beats/lifetime among mammals against life expectancy and body weight (allometric scale of 0.5 x 10(6)) are, within an order of magnitude, remarkably constant and average 7.3 +/- 5.6 x 10(8) heart beats/lifetime. A study of universal biologic scaling and mortality suggests that the basal energy consumption/body atom per heart beat is the same in all animals (approximately 10(-8) O2 molecules/heart beat). These data yield a mean value of 10 x 10(8) heart beats/lifetime and suggest that life span is predetermined by basic energetics of living cells and that the apparent inverse relation between life span and heart rate reflects an epiphenomenon in which heart rate is a marker of metabolic rate. Thus, the question of whether human life can be extended by cardiac slowing remains moot and most likely will only be resolved by retrospective analyses of large populations, future animal studies and clinical trials using bradycardic therapy.