We report a case of muscular dystrophy with thymoma that was detected by chance at the examination of his fatal arrhythmia. He has hypercapnea and restrictive pulmonary disfunction, but non-invasive positive pressure ventilation (NPPV) had not been introduced. Thymo-thymectomy was performed through reversed L-shaped mediansternotomy. NPPV was effective in his perioperative management.