Arrhythmogenic right ventricular dysplasia (ARVD) is a hereditary cardiomyopathy and a leading cause of sudden cardiac death (SCD) in the young and the athlete. Yet, risk stratification regarding the necessity of an ICD in this challenging disease needs further refinement. The occurrence of an acute phenomenon of superimposed myocarditis on top of ARVD may lead to acute devastating congestive heart failure (CHF) in some cases. Here, we report such a case in whom the clinical course was illustrated by release of troponin and progressive decrease in left ventricular ejection fraction (LVEF), and finally heart transplant confirming the diagnosis of ARVD, but also showing a typical involvement of both ventricles by histological signs of lymphocytic myocarditis. A male teenager with a negative family history for cardiomyopathies/sudden cardiac death (SCD) presented with palpitations after a football game. 12-lead ECG revealed left anterior hemiblock and a typical Epsilon wave in V1/V2 as opposed to the normal QRS duration in V5-V6. Four months later he had a documented episode of sustained ventricular tachycardia (VT) with left bundle branch block morphology (LBBB). Transthoracic echocardiography (TTE) showed major dilatation of both right ventricle and right atrium associated with regional wall motion abnormalities. However, initially LV size and LVEF were normal. Signal-averaged ECG was pathologic, and ventricular contrast angiography was typical of ARVD. Cardiac magnetic resonance tomography (CMR) confirmed RV dilatation and thinning and akinesia of the RV free wall. VT was not inducible at electrophysiological study at baseline, but a torsade de pointes-like ventricular tachyarrhythmia followed by LBBB VT was observed after isoproterenol challenge. Some days later, the patient had chest pain, increase in troponin level and T waves changes in the inferior leads. Viral serology was positive for parainfluenza III. Two months later, frequent premature ventricular contractions (PVCs), and three months later non-sustained episodes of VT occurred, and viral serology remained positive for parainfluenza. At this time, LVEF was preserved with 57%. However, abrupt disease progression was observed three months later. Severe VT occurred during exercise necessitating direct current cardioversion. A major increase in troponin levels reached 120 ng/ml. An ICD was implanted subsequently. After nine months multiple episodes of VT with LBBB morphology and superior axis were associated with clinical signs of progressive RV failure. Further dilatation of the RV and a decrease in LVEF to 45% occurred, as well as signs of hepatic dysfunction due to right-sided congestion. Few months later congestive heart failure was associated with an LVEF of 25%. Clots in the LV were observed with probable coronary emboli. Successful heart transplantation was performed. Gross pathology showed evidence of typical ARVD. Microscopic examination exhibited clusters of lymphocytes in the RV. The same pattern was observed in the LV with multiple foci of lymphocytes, associated with areas of myocardial necrosis and chronic-active fibrosis (Figure). This case is well in line with the recent work of Lopez-Ayala (Heart Rhythm. 2015; 12: 766–73.) confirming the suggested association of ARVD with superimposed myocarditis, leading to rapid disease progression eventually necessitating cardiac replacement therapy, and could be based on a common genetic susceptibility for myocarditis in patients with ARVD. Unfortunately, genetic information was not available in this case (Dr F Roland, Medical Thesis, University of Toulouse 2002).