Determining termination of an identified tachyarrhythmia episode may involve analysis of a relative decrease in tachyarrhythmia rate, a normalization of electrogram morphology criteria, or both. An implanted medical device may obtain a tachyarrhythmia rate and a morphology of a cardiac waveform. The device may compare the tachyarrhythmia rate to a threshold tachyarrhythmia rate and the morphology to a template morphology, and classify the heart beat as indicating termination of the tachyarrhythmia episode when the tachyarrhythmia rate is less than the threshold tachyarrhythmia rate, the morphology categorizes as normal, or both. For arrhythmias with no therapy delivered, observation of arrhythmia behavior at the point of termination may lead to improved classification. In addition, observation of a relative decrease in tachyarrhythmia rate immediately after therapy application can lead to application of slower but more specific criteria for redetection. Also, delivery of cardioversion shocks can be aborted upon tachyarrhythmia termination.