An active implantable medical device of the defibrillation/cardioverter type able to detect a post-therapy sinusal tachycardia. This device includes circuits and logic able to detect ventricular and atrial activity; episodes of tachycardia and deliver a therapy for defibrillation and/or cardioversion, and/or antitachycardia stimulation. The detected tachycardia are classified, and there is selective control for the delivery of therapy according to the type of detected tachycardia classified. The device conducts further analysis of tachycardia after delivery of a shock therapy and is able to determine the presence of a post-therapy sinusal tachycardia, preferably by recognition of a stable ventricular rate, a 1:1 association of ventricular and atrial rates, a ventricular heart rate that is located in a range corresponding to a slow ventricular tachycardia. The device also is able to inhibit the delivery of a therapy in the presence of determined post-therapy sinusal tachycardia.