<prompt> Action potential in cardiac muscles is due to which ions-KNaCa2C1-  <response>: Ans. is b a c i.e., Na K Ca2 Na, K and Ca2, all are involved in full cycle of action potential in cardiac muscle. But, the main phase phase 0 or depalarization is due to Na ions. Phase 0 phase of rapid depolarization - opening of fast sodium channels with Na influx. Phase 1 initial phase of rapid repolarization - closure of fast sodium channels. Phase 2 plateu phase - opening of voltage gated slow Ca channels with calcium influx. Phase 3 final repolarization - opening of K channels with K efflux. Phase 4 - Resting membrane potential. 