Antiarrhythmic medications used for Premature Ventricular Contractions (PVCs) primarily function by modulating cardiac ion channels to stabilize myocardial excitability and conduction. Class I agents block sodium channels to reduce phase 0 depolarization, decreasing ectopic ventricular activity, while Class III agents prolong repolarization by blocking potassium channels, increasing the refractory period to prevent abnormal automaticity.