Cardiac workload is influenced by which factors?

• A. Only preload
• B. Only afterload
• C. Stroke volume alone
• D. Preload, Afterload, and Heart Rate

Answer: (D)

Cardiac workload, or the heart’s energy expenditure per unit time, rises when the heart works harder in any of several ways. Preload increases the volume and pressure in the ventricles at the end of filling; more filling stretches the myocardial fibers, which raises wall tension and oxygen demand. Afterload is the pressure the ventricle must generate to open the aortic (or pulmonary) valve; higher afterload makes the heart work harder to eject blood, increasing workload. Heart rate adds workload directly by increasing the number of contractions per minute, so the heart uses more energy overall.

Stroke volume, while central to how much blood is moved with each beat, is not a separate factor that determines workload by itself. It’s a result of preload, afterload, and contractility, and it reflects output rather than being an independent driver of the heart’s energy demand. Therefore the factors that influence cardiac workload are preload, afterload, and heart rate.