“. . . the fundamental object of contention in the life struggle(sic), in the evolution of the organic world, is available energy.”
Ludwig Boltzmann (1886)
The title seems awkward, like the subject matter. Not that it helps, but, it could have been worse, as sometimes appears in the medical literature, “Longevity and Heart Beats in Man(sic).” I make no claim to being completely non-sexist, but come-on clinicians…”in Man(sic)?”
So what am I talking about? It appears empirically that we as humans, like many mammals, are given a set amount of heart beats in our lifetime.
No one really know why, and even that number is debatable still. But that statistic, like most statistics in the new science of “Medicine”, comes from evidence-based analysis. I list my URL and PDF references supporting this statistic below, in no particular order weened from Google Scholar©.
Many clinical researchers, like The Heart Rate Working Group of Kim Fox, Jeffrey S. Borer, A. John Camm, Nicolas Danchin, Roberto Ferrari, Jose L. Lopez Sendon, Philippe Gabriel Steg, Jean-Claude Tardif, Luigi Tavazzi, and Michal Tendera find that heart rate is an independent predictor of mortality of all humans with or without heart disease.
Let me type that again, but “louder”,
RESTING HEART RATE IS AN INDEPENDENT PREDICTOR OF MORTALITY FOR ALL HUMANS WITH AND WITHOUT HEART DISEASE
Or in a “whisper”, in our best bedside manner:
“Recent large epidemiologic studies have confirmed earlier studies that showed resting heart rate (HR) to be an independent predictor of cardiovascular and all-cause mortality in men and women with and without cardiovascular disease. Clinical trial data suggest that HR reduction is an important mechanism of benefit of beta-blockers and other HR lowering drugs. Pathophysiological studies indicate that a relatively high HR has direct detrimental effects on the progression of coronary atherosclerosis, on the occurrence of myocardial ischemia and ventricular arrhythmias, and on left ventricular function. Studies have found a continuous increase in risk with HR above 60 beats/min.” 
How Many Heart Beats, roughly, are Humans given?
Actually, the short answer is three billion. 3,000,000,000 heart beats plus or minus a a few hundred million. As in “billions and billions of stars” – Carl Sagan. That number creates a statistical line with all other air-breathing, baby-popping, milk-feeding mammals ( Figure 2). 
The five stages: denial, anger, bargaining, depression and acceptance
Look, when I became aware of this three (3) billion heart beat number, I have had discussions with many friends, and strangers. The worst was with an ICU nurse in the Atlanta Jackson-Hartsfield International Airport over Memorial Day. “Well son,” (thinking I was younger than her), “I have border-line tachycardia,” in her lilting white-Atlanta-accent, “of ninety beats per minute. I am 57 years old and I should be dead by that standard.” Hmmm, I hate those kind of conversations.
We all have stories. Stories are good. We all have anecdotal information that will – in our own mind – buy us another billion heart beats. Sorry. It’s sorta like global warming. It’s not an opinion and if you do not hold it, then it doesn’t affect you. Global warming affects us all. It is the main issue affecting all of us and we can act on it. Unfortunately, total heart beats affect us individually, and it is hard for us to influence our resting heart rate, if at all.
If I think I can stand the hassle I will write on this subject again. However, I want all of you to read what I have read who wish to debate. It’s ALL there. Just read it. Bye for now!
 Journal of the American College of Cardiology,
 Circulation EDITORIAL: Exercise, Heart Rate Variability, and Longevity, The Cocoon Mystery? Paul Poirier, MD, PhD, FRCPC 2085, (2014).