A sophisticated MRI imaging technique shows the orientation of the muscles of a mouse heart, with the different colors indicating the direction of the individual muscle fibers. It reveals that the muscles form a spiral, allowing the heart to efficiently relax and contract. The mouse’s heart contracts about 500-700 times per minute, about a billion beats in three years—the life expectancy of a lab mouse. Interestingly, many other mammal species have a similar number of heartbeats in their lifetimes. For example, the human heart beats about 70 to 80 times per minute—around three billion heartbeats in 75 years. In general, there is a rough relationship between heartbeat and body size, with larger animals tending to have slower heartbeats, but larger animals also tend to live longer—so it evens out.
The heart was dissected from a perfusion-fixed mouse and immersed in a solution to enhance the MRI signal and imaged using high-resolution MRI diffusion tensor imaging (DTI). The mouse heart’s size is about 12 mm from the base to the apex.
Image courtesy of Luke Xie PhD, Russell Dibb PhD, G. Allan Johnson PhD, Center for In Vivo Microscopy, Duke University Medical Center, Durham, NC and Chunlei Liu PhD, Brain Imaging and Analysis Center, Duke University Medical Center, Durham, NC.