Successful percutaneous balloon mitral valvuloplasty was performed in six patients utilizing single large (up to 30 mm diameter) balloons. Mitral valve area increased from 1.1 +/- 0.1 to 2.5 +/- 0.3 cm2 (P less than 0.01), and there were no complications or significant increases in mitral regurgitation. Single large-balloon mitral valvuloplasty may be as effective as the currently used double-balloon technique and may allow the procedure to be performed more easily and quickly.