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The total resistance against which blood must be pumped is known as afterload. Afterload is a critical factor in understanding cardiac function, as it represents the pressure that the heart must overcome to eject blood during systole. It is influenced by factors such as systemic vascular resistance and the elasticity of the arteries. A higher afterload means the heart has to work harder to pump blood, which can affect cardiac output and overall cardiovascular health.

In the context of cardiovascular dynamics, preload refers to the volume of blood in the ventricles at the end of diastole, rather than resistance. Cardiac output is the total volume of blood the heart pumps per minute, and stroke volume is the amount of blood ejected by the heart with each beat. While these terms are all interrelated in the study of hemodynamics, afterload specifically focuses on the resistance faced by the heart when it pumps, making it the correct choice in this context.