Final answer:
Potassium channel blockers, such as amiodarone and procainamide, affect the repolarization phase of the action potential in the heart by blocking the movement of potassium ions through voltage-gated channels.
Step-by-step explanation:
Potassium channel blockers, such as amiodarone and procainamide, are class IV antiarrhythmics used to treat abnormal electrical activity in the heart. They work by impeding the movement of potassium ions (K+) through voltage-gated K+ channels. By blocking these channels, these medications affect the repolarization phase of the action potential, prolonging its duration.