The study was published in Frontiers of Physiology. It focused on comparative differences between elite-level runners and swimmers. The study found that different activities produce anatomical, physiological, and functional differences in the heart over time.
The fact that differences exist in practitioners of different sports makes intuitive sense. In general terms, the study found that athletes in both runner and swimmer groups posessed remarkable heart health; resting heart rate of all study subjects was around 50 beats per minute and all subjects had relatively large, efficient left ventricles. More specifically, however, the study found that running is associated with faster left ventricle untwisting during diastole and enhanced early diastolic filling.