What is the mechanism of action for calcium channel blockers?

Calcium channel blockers primarily work by inhibiting the entry of calcium ions into cardiac and smooth muscle cells. This reduced calcium influx leads to decreased contractility of the heart muscle, which lowers the workload on the heart. Additionally, in vascular smooth muscle, this inhibition causes relaxation and dilation of blood vessels, which helps to decrease blood pressure and reduce the demand for oxygen by the heart. This mechanism is particularly beneficial in conditions such as angina, where the heart requires more oxygen but is unable to obtain it due to narrowed coronary arteries.

The other options do not accurately describe the function of calcium channel blockers; they either suggest an increase in calcium levels in cells or do not pertain to the key action of these drugs. Thus, the correct response underscores the primary therapeutic action of calcium channel blockers in clinical practice.