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The shrew's resting heart rate can reach up to 17 beats per second, equivalent to about 1,020 beats per minute. In comparison, the average human resting heart rate is around 60 to 100 beats per minute, making the shrew's resting heart rate approximately 10–17 times higher than that of humans.

Until now, it has been a mystery how these small mammals achieve such an extreme resting heart rate, but a new study, just published in the journal Science, sheds light on the mystery.

An international research team led by postdoc William Joyce, during his time at Aarhus University (AU), and Professor Kevin Campbell, previously affiliated with AU and now at the University of Manitoba (Canada), has investigated how evolutionary changes in the heart protein "cardiac troponin I" have enabled shrews to achieve their unusually high resting heart rate.

"We discovered that a crucial part of the heart protein that regulates heart relaxation time is missing in shrews and closely related moles. This evolutionary loss permanently removes the brakes on heart relaxation, allowing their hearts to beat much faster," explains Joyce, now working at The Centro Nacional de Investigaciones Cardiovasculares Carlos III (CNIC) in Spain.

A missing DNA region

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