An operation to repair or reconstruct a defective heart valve (see VALVES). It may be done as an open-heart procedure (with the patient temporarily connected to a HEART-LUNG MACHINE that maintains the circulation of oxygenated blood) but the procedures are most frequently performed using a balloon-ended catheter (see CATHETERS) passed through the skin into a blood vessel and on to the heart. The balloon is inflated and the flaps of a narrowed (stenosed) valve are prised apart.