Which term describes the pressure that the heart must pump against to force blood out into circulation?

The term that describes the pressure the heart must pump against to force blood out into circulation is afterload. Afterload refers specifically to the resistance that the ventricles must overcome to eject blood during systole. It is impacted by factors such as vascular tone and the elasticity of the arterial walls, which affect the overall resistance in the systemic circulation. A higher afterload means the heart must exert more effort to pump blood, which can influence cardiac output and overall heart function.

In contrast, preload is the degree of stretch of the cardiac muscles prior to contraction, mainly determined by the volume of blood returning to the heart. Contractility refers to the inherent strength and vigor of the heart's contraction, which can be influenced by various factors including ion concentrations and hormonal effects. Loss of tone is not a standard term used in cardiology to describe hemodynamics; it generally relates to muscle or vascular tone in a broader context, rather than specifically addressing the resistance faced by the heart during blood ejection.