What does Starling's Law state about myocardial contraction?

Starling's Law, also known as the Frank-Starling mechanism, posits that the strength of myocardial contraction is directly related to the degree of stretch of the cardiac muscle fibers prior to contraction. Specifically, as the heart fills with blood during diastole, the myocardial fibers are stretched more. This increased stretch results in a greater force of contraction during systole. In other words, the more the myocardial muscle fibers are stretched, the more forcefully they can contract. Consequently, this mechanism allows the heart to adjust its output to match the volume of blood being returned to it, enhancing its efficiency in pumping blood throughout the body.

The other options do not accurately reflect this relationship. For instance, a decrease in heart rate with increased myocardial stretch contradicts the principle of Starling's Law. Similarly, stating that myocardial contraction is unaffected by preload and afterload misrepresents the foundational understanding of how these factors influence cardiac performance. Finally, the assertion that contraction strength decreases with lower stroke volume does not align with Starling's Law, as the strength of contraction is primarily influenced by fiber stretch, rather than the volume of blood in circulation.