When you compare the lifespans of mammals, it is common to see that larger animals live longer than smaller animals. Another observation is that smaller mammals almost always have a much higher basal heart rate. For example, a mouse has a basal heart rate of about 600 beats per minute (bpm), but only lives 3 years on average. An elephant has a basal heart rate of 30bpm, but lives up to 60 years. If you do the maths, it turns out that the total heartbeats per lifespan is surprisingly similar between the two species (0.94 billion beats). It has been noted that amongst mammals, there is a clear inverse correlation between heart rate and lifespan.
This observation led to the popularisation of a factoid that the heart can only beat a limited number of time before it eventually fails.
Unfortunately, there has been very limited evidence to support this theory. It is medically true that a heart under more strain for a long period of time, such as with high blood pressure, has a tendency to develop more diseases such as cardiomyopathy and heart failure. However, there are too many other variables to consider. For example, exercise temporarily raises your heart rate but improves your overall cardiovascular health and lowers your basal heart rate.
It is much more likely that death from aging is related to the basal metabolic rate. Metabolism produces free radicals, which are elements with free electrons that can damage cells. Therefore, the higher the metabolic rate (such as in mice), the faster the damage accumulates and results in death.
That being said, consider the other implication of the so-called heartbeat hypothesis. Our hearts beat faster in response to many stimuli: exercise, excitement, fear, anxiety, fun and love. If the hypothesis is true, that would mean that intense emotions could make our hearts tire out faster and hasten our inevitable demise.
Could falling in love be detrimental to our physical health? Thankfully, this has never been shown to be true, with many studies showing that happily married couples tend to outlive single people.
Even if it were true, would you give up on the idea of love to live a few more years? What kind of life would be worth living without any highs or lows? Perhaps when we fall in love, experience heartache or become overwhelmed with happiness, we are making the voluntary choice of quality, not quantity, of life.