AQA A Level PE – The Cardiovascular System Practice Test 2026 - Free Practice Questions and Study Guide

The key idea is the Frank–Starling mechanism: when venous return increases, the ventricle fills more during diastole, raising the end-diastolic volume. This extra stretch of the cardiac muscle fibers enhances their contractile force through the length–tension relationship, so the heart contracts more forcefully and ejects a larger stroke volume to match the increased filling. This is what Starling's Law describes—the link between preload (the filling) and the force of contraction. Preload explains the filling itself, while afterload is the pressure the heart must work against, and stroke volume is the outcome, not the mechanism described.