<prompt> Answer this question truthfullyWhat is the cause of Phase 1 of the myocardial action potential and what happens to the voltage-gated channels involved in this phase?  <response>: <reason> Phase 1 of the myocardial action potential is caused by inactivation of voltage-gated Na channels and opening of voltage-gated K channels. During this phase, the membrane potential rapidly repolarizes due to the efflux of K ions out of the cell, while the inactivation of Na channels prevents further influx of sodium ions. This allows the cardiac muscle cells to briefly relax before the next phase of the action potential. 