According to Starling's law of the heart, what primarily determines stroke volume?

Stroke volume, which is the amount of blood ejected by the heart with each beat, is primarily determined by venous return due to Starling's law of the heart, also known as the Frank-Starling mechanism. This principle states that the more the cardiac muscle fibers are stretched by incoming blood (venous return), the more forcefully they will contract, leading to a greater stroke volume.

When venous return increases, it causes the heart to fill more during diastole, stretching the myocardial fibers. This increased stretch enhances the contractile force during systole, resulting in a higher stroke volume. Thus, venous return directly influences the preload, which is a critical factor in determining how much blood the heart pumps out during each heartbeat.

Heart rate, while influential in determining cardiac output when combined with stroke volume, does not directly determine stroke volume itself. Blood pressure is a result of cardiac output and systemic vascular resistance but does not influence stroke volume in the context of Starling's law. Coronary perfusion primarily affects the heart muscle's oxygen supply and function but does not directly dictate stroke volume in the same manner as venous return does. Therefore, understanding the relationship between venous return and stroke volume is essential in cardiovascular physiology and perf