Pre-periodic contraction and normal contraction when the cardiomyocyte membrane potential changes are the same, if the ectopic stimulus falls in the previous contraction of the relative period of inactivity, so that the next contraction in advance, the whole membrane potential changes will be in advance, the normal rhythm is passed down the cardiomyocyte is in a state of euphoria, no effect, the cell membrane repotentiation, the distance from the next time the next normal rhythm is transmitted down the time is longer than the normal rhythmic intervals