A healthy 35-year-old male undergoes a physiological stress test. Which of the following best describes the primary mechanism by which an increase in end-diastolic volume leads to an increase in stroke volume?

The correct answer to the question "A healthy 35-year-old male undergoes a physiological stress test. Which of the following best describes the primary mechanism by which an increase in end-diastolic volume leads to an increase in stroke volume?" is Option B: Enhanced cross-bridge formation due to optimal sarcomere length.

The other options — A) Increased contractility due to sympathetic stimulation, C) Decreased afterload on the left ventricle, D) Increased heart rate — are incorrect for this USMLE Exam Prep question. As explained above: The Frank-Starling mechanism states that increased venous return leads to increased ventricular filling (end-diastolic volume), stretching cardiac muscle fibers to a more optimal length for actin-myo…