Emergency Medical Technician (EMT) Intermediate Practice Exam

According to Starling's law of the heart, what happens when there is an increase in diastolic filling?

1. Heart rate decreases

2. Contractility increases

3. Cardiac output decreases

4. Blood pressure decreases

The correct answer is: Contractility increases

Starling's law of the heart, also known as the Frank-Starling mechanism, states that when there is an increase in diastolic filling, or preload, the force of contraction of the heart muscle increases. This happens because as the ventricles fill with more blood during diastole, the cardiac muscle fibers stretch more. The increased stretch leads to a more forceful contraction during systole, which improves the heart's efficiency in pumping blood. Therefore, when there is increased diastolic filling, the contractility of the heart increases, leading to enhanced cardiac output, assuming other factors remain constant. This law is crucial for understanding how the heart adapts to varying volumes of blood and is fundamental in both normal physiology and in clinical settings where heart function is compromised.