Which of the following is a cardiovascular benefit of regular exercise?

Regular exercise has numerous cardiovascular benefits, one of which is enhanced cardiac efficiency. This means that the heart becomes more effective at pumping blood with each beat, resulting in improved circulation and oxygen delivery to the body's tissues. As cardiovascular fitness improves, the heart can supply the demands of physical activity with less effort, which can lead to a lower resting heart rate and reduced blood pressure over time. This is particularly beneficial because an efficient heart can help lower the risk of cardiovascular diseases and improve overall fitness levels.

In contrast, increased muscle mass, improved flexibility, and increased body fat percentage do not encompass the cardiovascular benefits associated with regular exercise. While increased muscle mass is a benefit of strength training, and improved flexibility contributes to overall physical fitness, these do not specifically relate to heart function and circulation. Increased body fat percentage is generally discouraged as it can lead to various health issues, including adverse effects on cardiovascular health.