One billion heartbeats

One of the defining features of mammals is the four chambered heart. A curiosity of biology is that all mammals have more or less the same lifespan, if you measure it in heartbeats: one billion beats, give or take a billion.

If you’re a large mammal, like an elephant, your heart beats slowly, and you live many years. If you’re a mouse, your tiny heart beats far faster, and you’re lucky to live more than a handful of years. If you’re a human, your heart usually beats around 70 times a minute. Mine is a little different. It likes to throw in an extra beat here and there.