Introduction: Sudden cardiac death is defined as that which occurs unexpectedly within the first hour after the onset of symptoms or if it occurs in the absence of witnesses when the deceased has been seen in good condition in less than 24 hours before of the recess. In this sentence the 3 characteristics are condensed: 1. natural phenomenon, 2. unexpected, 3. fast. The final event is a picture of cardiac electrical instability, which leads to lethal arrhythmia and within its cardiac causes arrhythmogenic right ventricular dysplasia exemplifies it. Case report: We present the case of a healthy school patient who after an adenotonsilectomy and without incidents during surgery, presented a cardiac MS, in her immediate postoperative period. Requesting a legal medical autopsy which concluded a arrhythmogenic right ventricular dysplasia. Cardiovascular pathology unknown in the preoperative for the surgical team, evidenced as a postmortem finding. Conclusion: Although it is true that arrhythmogenic right ventricular dysplasia is an infrequent cardiovascular pathology, it must be considered and discarded before any surgical procedure, due to the outcome that this can cause. Therefore, we always suggest having a targeted cardiovascular anamnesis and requesting an electrocardiogram as part of the Pre-Surgical Protocol and, if it is pathological, refer to a cardiological study. Consider arrhythmogenic right ventricular dysplasia as a diagnosis to rule out against cardiac MS.