Which statement is true regarding myocardial functioning in the normal heart, based upon the Frank Starling law?

A) An increase in afterload results in decreased systolic pressure, which creates a decreased cardiac output: This statement is incorrect. According to the Frank-Starling law, afterload refers to the resistance against which the heart must pump blood during systole. An increase in afterload typically results in increased systolic pressure, not decreased, as the heart works harder to overcome the increased resistance. However, increased afterload can lead to decreased cardiac output due to the increased work of the heart. B) A decrease in afterload causes the cardiac muscles to hypertrophy, resulting in increased diastolic volume: This statement is incorrect. A decrease in afterload typically reduces the workload on the heart, which may lead to reverse remodeling and a reduction in cardiac hypertrophy. Increased diastolic volume may occur due to reduced afterload, but it's not the direct result of hypertrophy. C) An increase in preload results in greater shortening of myocardial fibers, thereby increasing contractility: Correct. The Frank-Starling law states that an increase in preload (end-diastolic volume or stretch of myocardial fibers) leads to greater overlap of actin and myosin filaments within myocardial fibers during systole. This increased overlap results in stronger myocardial contraction (increased contractility), leading to an increased stroke volume and cardiac output. D) A decrease in preload results in increasing diastolic muscle fiber length, which impedes contractility: This statement is incorrect. Preload refers to the degree of stretch of the myocardial fibers at the end of diastole. A decrease in preload would lead to decreased stretch of the myocardial fibers, not increasing diastolic muscle fiber length. Decreased preload typically results in decreased contractility rather than an impediment to contractility due to reduced myocardial stretch.