What is the pressure against which the heart must work to eject blood during systole?

The correct choice is the one that describes the pressure against which the heart must work to eject blood during systole, known as afterload. Afterload refers to the resistance or pressure that the left ventricle must overcome to distribute blood into the aorta and through the systemic circulation. It is influenced by factors such as the diameter and elasticity of the arterial vessels, systemic vascular resistance, and overall blood pressure.

Understanding afterload is crucial for assessing cardiac function, particularly in conditions where the heart may struggle to pump effectively, such as in hypertension or heart failure. Elevated afterload can increase the workload on the heart, potentially leading to hypertrophy or other cardiac complications over time.

In contrast, preload is related to the volume of blood in the ventricles at the end of diastole and influences stroke volume through the Frank-Starling mechanism. Myocardial resistance is not a standard term used in cardiac physiology, and stroke volume specifically refers to the amount of blood pumped by the heart with each beat, which is affected by both preload and afterload but does not directly answer the question regarding the pressure faced during systole.