Which of the following changes occurs in the heart as a result of endurance training?

Endurance training leads to a variety of adaptations in the cardiovascular system, one of the most significant being an increase in the size of the ventricle. This enlargement, specifically of the left ventricle, occurs because the heart must pump a larger volume of blood to supply the working muscles during prolonged aerobic exercise. As the heart adapts to the increased demand for oxygen and nutrients, it becomes more efficient at pumping blood, which is beneficial for overall cardiovascular health and athletic performance.

This increase in the ventricular size can enhance stroke volume—the amount of blood pumped with each heartbeat—allowing athletes to perform better with less effort. Over time, this adaptation contributes to improved cardiovascular efficiency and endurance capacity. Moreover, this enlargement of the ventricle is typically accompanied by other positive changes in heart structure and function, including a greater capacity for blood flow and increased mitochondrial density in heart tissue.

While lower heart rates and other adaptations may occur with endurance training, the primary and most direct change relating to heart structure is the increase in ventricle size, which optimizes the heart's ability to sustain prolonged physical activity.