Emergency Medical Technician (EMT) Intermediate Practice Exam

According to Starling's Law of the Heart, what happens to contractility?

1. It decreases as myocardial walls are stretched

2. It remains constant regardless of wall stretch

3. It increases as myocardial walls are stretched

4. It becomes erratic with severe stretching

The correct answer is: It increases as myocardial walls are stretched

In the context of Starling's Law of the Heart, as myocardial walls are stretched (which occurs with increased ventricular filling or preload), the contractility of the heart muscle also increases. This principle states that the greater the stretch of the cardiac muscle fibers, the more forcefully they will contract, up to a certain limit. This relationship is crucial for maintaining adequate cardiac output, especially as the body's demand for blood changes. When the heart fills with more blood, the myocardial fibers stretch due to the increased volume, and this stretching leads to more significant force generation during contraction. This mechanism allows the heart to pump an adequate volume of blood to match venous return, thereby efficiently adjusting to varying physiological conditions without compromising blood flow. Other potential responses do not accurately reflect the physiological principles laid out by Starling's Law; they either misinterpret the relationship between stretch and contractility or do not align with the observable behavior of the heart under different loading conditions. Understanding this concept is vital for EMTs as it relates to patient assessments and interventions regarding cardiac function.