A 47-year-old woman who had been operated on 30 years earlier for a membranous type of subvalvular aortic stenosis presented with acute lung edema, rapid atrial fibrillation, and clinical signs of mitral regurgitation. Radiography of the thorax showed enlargement of the left cavities and signs of pulmonary congestion. Echocardiography revealed dilated left cavities, preserved left ventricular ejection fraction, and severe eccentric mitral regurgitation. This was confirmed by angiography that showed normal coronary arteries. At surgery, the mitral valve was found to have a perforation of approximately 1 cm in the anterior leaflet at the mitral-aortic continuity, and fibrous thickening of the leaflets with retraction of the free edges (Figure 1). The anterior mitral leaflet was resected and a prosthesis was implanted with sutures in the anterior section of the ring, placed around the upper area of the circular defect, achieving closure. Surgical resection of the aortic subvalvular fibrous ring (at the base of the septal mitral leaflet) may be complicated by mitral regurgitation through mitral valvular and mitral-aortic continuity lesions, even late after intervention.