Arrhythmogenic right ventricular dysplasia (ARVD) is a rare cardiomyopathy characterized by the progressive replacement of cardiomyocytes by fatty and fibrous tissue in the right ventricle (RV). These infiltrations lead to cardiac electrical instability and ventricular arrhythmia. Current treatment for ARVD is empirical and essentially based on treatment of arrhythmia. Thus, there is no validated treatment that will prevent the deterioration of the RV function in patients with ARVD. The investigator's hypothesis is that the use of anti-fibrotic medications will prevent or at least reduce the deterioration of the RV function. The aim of this project is to evaluate the effect of spironolactone, a Potassium-sparing diuretic on ventricular myocardial remodeling and on arrhythmia burden in patients with ARVD. The trial is a double-blind parallel multicenter prospective randomized phase II drug study. Patients will be randomized in the two groups: spironolactone or placebo. 13 centers in France will enroll the 120 patients (60 per group). Patients will be followed for 3 years (6 months, 1 year and 3 years) with all examinations (ECG, HA ECG, 24-hour Holter, trans-thoraciqc echocardiography (TTE), biological analyses) according to standard of care. A decrease in right and/or left ventricular deterioration and in arrhythmia burden are expected in ARVD patients treated with spironolactone. This reduction will improve the quality of life of patients and will reduce the number of hospitalizations and the risk of terminal heart failure.