What happens when end-diastolic volume increases according to Starling's law?

When end-diastolic volume increases, the heart muscle fibers are stretched more due to the greater volume of blood filling the ventricles during diastole. According to Starling's law of the heart, this increased stretch leads to a stronger contraction of the cardiac muscle during systole. As a result, the stroke volume—the amount of blood ejected from the heart with each beat—will increase. Therefore, the correct answer is that stroke volume increases as a response to higher end-diastolic volume.

This physiological principle demonstrates the relationship between the volume of blood returning to the heart and the strength of cardiac contraction. As the heart fills more with blood, its pumping ability improves, thereby enhancing overall cardiac output to meet the body’s demands.