refractory period, the time from phase 0 to the end of phase 3 of the action potential, divided into effective and relative. In pacing terminology, the period during which a pulse generator is unresponsive to an input signal of specified amplitude. The effective refractory period is from phase 0 to approximately −60 mV during phase 3 of the action potential, a time during which it is impossible for the myocardium to respond with a propagated action potential, or even to a strong stimulus. The relative refractory period is from approximately −60 mV during phase 3 to the end of phase 3 of the action potential, the time during which a depressed response is possible to a strong stimulus. Also called refractory phase, refractory state.
