Which statement correctly describes cardiac output and stroke volume determinants?

• A. Cardiac output equals mean arterial pressure times systemic vascular resistance.
• B. Cardiac output = heart rate × stroke volume; stroke volume is determined by preload, afterload, and contractility (and heart rate to an extent).
• C. Cardiac output equals heart rate plus stroke volume; stroke volume is determined by preload only.
• D. Cardiac output is dependent on heart rate only; stroke volume is constant.

Answer: (B)

Understanding how cardiac output is set in the heart means looking at both how often the heart beats and how much blood is moved with each beat. The statement that correctly captures this is that cardiac output equals heart rate multiplied by stroke volume. Stroke volume, in turn, is determined by preload (the filling of the ventricle), afterload (the pressure the ventricle must work against), and contractility (the strength of the ventricular contraction). Heart rate also influences stroke volume indirectly—faster rates shorten the filling time and can modestly affect preload, but the main players for stroke volume are preload, afterload, and contractility.

Putting it together, the product of heart rate and stroke volume gives the cardiac output; stroke volume depends on how much the ventricle fills, how hard it must push, and how strongly it contracts (with some influence from heart rate). This is why the described relationship is the best, whereas alternatives that mix up multiplication with addition or swap in MAP and SVR incorrectly describe the fundamental connections.