Exploring left ventricular isovolumic shortening and stretch mechanics: "The heart has its reasons...".

A rifle recoils when fired. This recoil is the result of action-reaction force pairs. Consistent with Newton’s third law of motion, as the bullet is propelled, it pushes backward upon the rifle. Similar sequences appear in the heart, nature’s most efficient propulsion design. The early activated regions of the left ventricle (LV) shorten, forcing blood to accelerate (1). But an equal and opposite force produces a backward thrust that is felt over the chest wall as