1. An implantable system, comprising: electrodes configured to electrically couple to a heart; a pulse generator coupled to the electrodes, the pulse generator configured to deliver electrical therapy for the heart; a sensing system coupled to the electrodes and configured to sense a cardiac signal associated with delivery of electrical therapy to the heart using the electrodes; and circuitry configured to manage capture testing, the circuitry configured to acquire a post-therapy evoked response signal subsequent to delivery of a high energy therapy using signals received from the sensing system, compare a baseline evoked response template and the post-therapy evoked response signal, determine whether the high energy therapy rendered myocardial tissue of the heart unstable based on the comparison, and determine whether to enable, disable or adjust capture testing based at least in part on whether the high energy therapy rendered myocardial tissue of the heart unstable.