AEMCA Practice Exam

What effect does running blockade of calcium channels have on cardiac function?

1. Increases heart rate

2. Decreases force of contraction

3. Relaxes vascular smooth muscle

4. Potentiates adrenaline effects

The correct answer is: Relaxes vascular smooth muscle

Running a blockade of calcium channels primarily decreases the influx of calcium ions into cardiac and vascular smooth muscle cells. Calcium is crucial for various cardiac functions, including the contraction of heart muscle and muscle tone in blood vessels. When calcium channels are blocked, there is a significant reduction in the force of contraction of the heart muscle. This is because calcium ions are essential for the excitation-contraction coupling process in cardiac tissue. Therefore, the force with which the heart contracts is diminished, leading to decreased cardiac output. While relaxing vascular smooth muscle is a correct consequence of calcium channel blockade, the effect on cardiac function primarily involves a decrease in the force of contraction rather than an increase in heart rate or potentiation of adrenaline effects. The relaxation of vascular smooth muscles can result from such blockades, leading to vasodilation and ultimately reduced blood pressure. This mechanism can be beneficial in treating conditions like hypertension but does not directly reflect the primary effect on cardiac contractility as seen in the heart. In summary, while relaxing vascular smooth muscle is a true outcome of calcium channel blockade, the direct focus on heart function emphasizes the importance of decreasing the force of contraction as a key physiological change.