The primary function of the heart in terms of fitness is to pump oxygenated blood throughout the body, delivering nutrients to muscles and organs during physical activity. A strong, efficient heart can improve exercise performance by supplying the necessary energy for muscle contractions. Regular cardiovascular exercise strengthens the heart, promoting better circulation and reducing resting heart rate. This efficiency translates into improved endurance, allowing individuals to engage in longer durations of physical activity while minimizing fatigue and strain on the cardiovascular system.