Final answer:
Class III antiarrhythmics like amiodarone and procainamide block potassium channels to prolong the action potential's plateau phase, increasing its duration and helping stabilize the heart's electrical activity.
Step-by-step explanation:
Class III antiarrhythmics, such as amiodarone and procainamide, work by blocking K+ channels, thereby impeding the movement of potassium ions through voltage-gated potassium channels in the heart. This action prolongs the plateau phase of the cardiac action potential and increases the duration of the action potential. By lengthening the refractory period, these drugs help to stabilize abnormal electrical activity in the heart, known as cardiac dysrhythmia, and prevent rapid re-activation of the heart's electrical system, which can lead to arrhythmias.
Potassium channel blockers primarily affect the repolarization phase of the cardiac action potential. During repolarization, the blocked potassium channels cause a delay in returning the cardiac cells to their resting state. This delay helps in the treatment of various ventricular and atrial arrhythmias by ensuring that the heart cells do not become excessively excitable. However, these drugs require careful monitoring due to the potential for side effects and toxicity, especially if used long-term.