Final answer:
Potassium channel blockers, such as amiodarone and procainamide, affect the repolarization phase of the cardiac action potential.
Step-by-step explanation:
Potassium channel blockers, such as amiodarone and procainamide, are used to treat abnormal electrical activity in the heart. These medications impede the movement of K+ through voltage-gated K+ channels, affecting the repolarization phase of the cardiac action potential.