Cardiac remodeling in endurance athletes is proportional to training volume and duration, with the most pronounced changes observed in male athletes engaged in long-term, high-volume endurance sports such as cycling, rowing, and long-distance running.

Repeated long-duration exercise pushes more blood into the heart, stretching the heart chambers over time. This stretch triggers the heart muscle to grow longer instead of thicker, making the chambers bigger to hold more blood. The heart also learns to relax faster and refill more efficiently between beats by improving how it handles calcium inside its cells. The upper chambers enlarge too, helping the heart fill better during fast heart rates. These changes are strongest in men who train heavily for many years.