What effect do calcium channel blockers like verapamil have on the heart?

Calcium channel blockers, such as verapamil, primarily exert their effects on the cardiovascular system by inhibiting the influx of calcium ions during depolarization of the cardiac muscle cells. This action leads to a reduction in the force of contraction (contractility) of the heart because calcium is essential for myocardial contraction. Additionally, calcium channel blockers have a direct effect on the sinoatrial (SA) and atrioventricular (AV) nodes, which slows down conduction and leads to a decrease in heart rate.

When these medications are administered, the diminished availability of calcium reduces both the heart's contractility and its overall rate, making verapamil particularly effective for conditions like hypertension and certain types of arrhythmias. Thus, the option that states calcium channel blockers like verapamil decrease both contractility and heart rate accurately reflects their pharmacodynamic profile.