Heart rate does have a lot to do with it. House cats have a heart rate of around 150 beats per second, so they live around 4 times as long as mice.
You are correct that humans should have a life expectancy of 21 years based on their heart rate. In fact, many mammals having a heart rate of around 70, such as lions and tigers, do live around 21 years. However, primates in general, not just humans, have hearts that last about 3 times as long as most mammals, not just mice. Our hearts and the hearts of other primates can beat 3 times as long before failing. Therefore, we live to over 60 and the chimpanzee also lives to as long as 45-50 years old in the wild, despite having a heart rate of 120 beats per minute. Monkeys that are the size of house cats live much longer than the house cats. The White-headed capuchin has a life span of up to 40 and yet it is about the same size as a cat.
Further, birds also have longer life expectancies than mammals. A hummingbird has a similar heart rate as mice, but hummingbirds live longer than mice, up to 12 years in captivity. No mice has ever lived that long in captivity. Hummingbirds only live 3-6 years in the wild (but that is still longer than mice in captivity) because of dangers from predators, such as house cats. Also, many ectotherms live longer lives in general than endotherms because they have lower metabolic rates, since their bodies do not have to generate heat constantly to replace heat that is lost to the environment. We all know how long turtles live, but even a small snake or frog can live well over a decade in captivity. Exercise makes the heart stronger, so athletes, unless they have genetic defects or they are substance abusers (steroids for example), should live longer than couch potatoes.
You are correct that humans should have a life expectancy of 21 years based on their heart rate. In fact, many mammals having a heart rate of around 70, such as lions and tigers, do live around 21 years. However, primates in general, not just humans, have hearts that last about 3 times as long as most mammals, not just mice. Our hearts and the hearts of other primates can beat 3 times as long before failing. Therefore, we live to over 60 and the chimpanzee also lives to as long as 45-50 years old in the wild, despite having a heart rate of 120 beats per minute. Monkeys that are the size of house cats live much longer than the house cats. The White-headed capuchin has a life span of up to 40 and yet it is about the same size as a cat.
Further, birds also have longer life expectancies than mammals. A hummingbird has a similar heart rate as mice, but hummingbirds live longer than mice, up to 12 years in captivity. No mice has ever lived that long in captivity. Hummingbirds only live 3-6 years in the wild (but that is still longer than mice in captivity) because of dangers from predators, such as house cats. Also, many ectotherms live longer lives in general than endotherms because they have lower metabolic rates, since their bodies do not have to generate heat constantly to replace heat that is lost to the environment. We all know how long turtles live, but even a small snake or frog can live well over a decade in captivity. Exercise makes the heart stronger, so athletes, unless they have genetic defects or they are substance abusers (steroids for example), should live longer than couch potatoes.
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In animals they are not, relatively speaking. All mammals (and some others) have a certain number of heartbeats and respiratory breaths (4 heart beats to 1 breath). When we use these up, we expire. The faster your heart beats, the shorter you live. The slower your heart beats, the longer you live. This is why speed freaks (people who use chrystel meth, etc.) look older then their years, and die younger.
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it all depends on their morphological make up and free radical excretion.