ACSM Certified Exercise Physiologist (EP-C) 2026 – 400 Free Practice Questions to Pass the Exam

The Frank Starling Law of the Heart explains that the heart’s stroke volume (the amount of blood pumped by the left ventricle in one contraction) is influenced by the volume of blood filling the heart before contraction, known as end-diastolic volume (EDV). According to this principle, as the EDV increases, the myocardial fibers are stretched more, leading to a more forceful contraction due to optimal overlap of actin and myosin filaments. This increased stretch enhances the heart’s ability to pump blood.

Thus, if the end-diastolic volume doubles, this means there is significantly more blood in the ventricles at the end of diastole. As a result, the heart attempts to pump this larger volume more effectively, which typically leads to an increase in stroke volume. Therefore, doubling the EDV leads to a proportional increase in stroke volume, reflecting the heart's capacity to adapt to varying levels of venous return, aligning with the Frank Starling Law.

This understanding is crucial in clinical and exercise settings, as it illustrates how the heart responds to increased venous return, enhancing cardiac performance during physical activity or in response to fluid overload.