The question refers to domestic cats. The adult cat’s normal heart rate is 142 to 240 bpm and the mean is 195 bpm (beats per minute).
For newborn kittens the heart rate is from 200 to 300 bpm at birth and approximately 200 bpm at two weeks of age.
It is noticeable that the heart rate of the domestic cat is much higher than that of humans. This begs the question as to whether the higher heart rate is the reason why the lifespan of a domestic cat is much shorter than that of a human.
If, in mammals, there is a maximum number of heartbeats that is available to a heart then if the heart beats at a higher rate the lifespan of that animal will be shorter.
It seems that the total, lifetime number of beats of the heart of a mouse is the same as that of a human except that the heart rate of mice is somewhere around 600 bpm and the lifespan is a couple of years. This formula does not quite work because if the domestic cat’s heart beats at three times the rate of a human heart he/she could live three times longer to 3×18=54 years if the rate was the same as a human’s. This is too short.
It’s physics. Things don’t operate exactly to scale. The forces of nature don’t affect matter of different sizes the same way.