Final answer:
Increased afterload leads to a higher systolic pressure in the pressure-volume loop due to greater resistance which the ventricles must overcome to eject blood, potentially decreasing stroke volume if the heart cannot compensate.
Step-by-step explanation:
What effect does increased afterload have on the pressure-volume loop? Increased afterload in the cardiovascular system leads to a greater resistance against which the ventricles must pump blood. When afterload increases, the pressure within the ventricles must rise higher before the semilunar valves open, causing a higher systolic pressure on the pressure-volume loop. This means that the phase of isovolumetric contraction is prolonged, and the volume of blood ejected during systole (stroke volume) may decrease if the ventricles cannot compensate adequately. Over time, if the afterload remains high and the heart cannot adjust, this situation can lead to a decrease in cardiac efficiency and potential heart failure. Factors like valve stenosis or hypertension can increase afterload, necessitating a higher ventricular pressure to open the aortic and pulmonary valves, accordingly shifting the pressure-volume loop upwards.