Aerobic exercise elevates your heartbeat while you’re doing it but slows it even more when you’re not doing it. So your fixed quota of heartbeats lasts longer (assuming there is a more or less fixed quota, which seems well-supported by evidence).

That sounds like…something an obscure ancient Greek philosopher would claim, leading Diogenes to start chasing him around the room counting down.

It kinda does… Not like, literally, but generally? In a statistical, mean time to failure kind of way? It’s surprisingly accurate

These people, like always, just take a nugget of truth and use it to come to wild conclusions. Because there’s a second, very important factor in this equation - exercise reduces your heart rate

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.

Here’s the study