ABSTRACTSubaortic stenosis is well known to complicate the clinical course of patients with single ventricle or univentricular hearts, and we have previously suggested that the development of subaortic stenosis in such patients may be causal to and/or accelerated by previous banding of the main pulmonary trunk. To further define the relationship between banding of the pulmonary artery in patients with univentricular hearts and the development of subaortic stenosis, we examined the morphologic substrate and timing of the development of subaortic stenosis in 43 patients seen at our institution from January 1, 1970, through June 30, 1985. These 43 patients include all patients in this period with an unequivocal univentricular heart whose longitudinal data was available for follow-up. We excluded patients who died within 1 week of surgery, patients lost to follow-up, and patients with evidence of subaortic stenosis before banding. Thirty-one of 43 patients (72. 1%) developed subaortic stenosis subsequent to banding of the main pulmonary artery. The mean age at banding of those patients who developed subaortic stenosis was 0.21 years, and subaortic stenosis was recognized at a mean age of 2.52 years. For the specific cohort of patients whose ventricular morphology was a main chamber of left ventricular type supporting the pulmonary artery and a rudimentary right ventricle supporting the transposed aorta (32 patients), 27 developed subaortic stenosis (84.4%). Subaortic stenosis in the classic form of single ventricle usually results from progressive restriction of a wholly muscular interventricular communication. Banding of the pulmonary artery by producing myocardial hypertrophy undoubtedly accelerates the potential for subaortic stenosis in these patients. Furthermore, one must realize that subaortic stenosis may be present in the absence of a resting pressure gradient, and such subaortic stenosis can usually be unmasked by stimulation with isoprenaline. Finally, one must be guarded in advocating banding of the pulmonary artery in patients with single ventricle, realizing that subaortic stenosis strongly influences the outcome of more definitive surgery in these patients.