Cardiovascular physiology: a free MRCS Part A question

The loop shows the response to an isolated rise in afterload. The ventricle must reach a higher pressure before the aortic valve opens, so ejection starts later and ends earlier on the same end-systolic pressure–volume line: end-systolic volume rises, stroke volume (the width of the loop) falls, and the loop becomes taller and narrower. A lower end-systolic volume with a larger stroke volume is the response to reduced afterload or to a rise in contractility. The slope of the end-systolic pressure–volume relation is an index of contractility and is not altered by an α1-agonist. Over subsequent beats the retained volume raises end-diastolic volume and the Frank–Starling mechanism partially restores stroke volume, but that is a secondary adjustment, not the immediate change. Peak systolic pressure rises, not falls, with increased resistance. Reference: Ganong 26e; Guyton & Hall 14e.