2. Calcium channel blockers slow the movement of calcium into the cells of the heart and blood vessels. Since calcium causes stronger heart contractions, these drugs ease the heart's contraction and relax the blood vessels. They can cause dizziness, heart palpitations, swelling of the ankles, and constipation. Take them with food or milk and avoid grapefruit juice and alcohol because of possible interactions.What is the mechanism of action of calcium channel blockers?