Aortic regurgitation after left ventricular myotomy and myectomy. Five hundred twenty-five patients with hypertrophic cardiomyopathy underwent left ventricular myotomy and myectomy (LVMM) from 1960 to 1990. Four hundred ninety-six had nonregurgitant trileaflet aortic valves before LVMM. In 19 (4%) of these patients, aortic regurgitation developed after LVMM. Age of the 19 patients ranged from 10 to 58 years (mean age, 35 +/- 3 [+/- standard error of the mean]]. Seven were male and 12, female. Five patients underwent LVMM followed immediately by aortic valve replacement or valvuloplasty. Aortic regurgitation developed in 14 patients at a later date. The average New York Heart Association functional class improved from 3.2 +/- 0.1 to 1.3 +/- 0.1 (p less than 0.05, Student's t test) after operation. The average peak systolic left ventricular outflow tract gradient at rest and with provocation decreased from 65 +/- 8 to 14 +/- 5 mm Hg (p less than 0.05) and 108 +/- 9 to 45 +/- 7 mm Hg (p less than 0.05), respectively, 6 to 8 months after operation. Aortic regurgitation occurred in 7 of the 14 patients at 6 months or less after operation, and 3 required operative repair. In the other 7 patients, aortic regurgitation developed 3 years or more after LVMM, and 3 of them also required operative repair. All 12 patients in whom aortic regurgitation developed at operation or within 6 months postoperatively had either a very small aortic annulus (less than or equal to 21 mm, 5 patients), a low mitral-septal contact lesion (greater than or equal to 35 mm below the aortic annulus, 3 patients), or both (4 patients). 