<prompt> Inward flow of Na in heart leads to:Plateau phaseAction potentialRepolarizationNo change  <response>: Phase 0 depolarization, fast sodium channels open. When the cardiac cell is stimulated and depolarizes, the membrane potential becomes more positive. Voltage-gated sodium channels fast sodium channels open and permit sodium to rapidly flow into the cell and depolarize it. The membrane potential reaches about 20 millivolts before the sodium channels close.Key Concept:Influx of Na via fast Na channel leads of phase 0 or beginning of AP in myocardium.Reference: GUYTON AND HALL TEXTBOOK OF MEDICAL PHYSIOLOGY, THIRTEENTH EDITIONINTERNATIONAL EDITION page no111 