Late morbidity and death as a result of transplant-related coronary vascular disease is a major unresolved problem for heart transplant recipients. Treatment of discrete coronary lesions in transplanted coronary arteries with angioplasty may be beneficial, but the long-term outcome and factors affecting restenosis are not known. To determine the effects of angioplasty on coronary caliber and the correlates of late restenosis, we studied the results of 25 balloon angioplasty procedures for physiologically significant coronary artery stenosis (> 15 mm Hg translesional pressure gradient) in nine heart transplant recipients. All patients underwent repeat coronary angiography within 6 months of angioplasty. Angiograms were analyzed by the Reiber-CAAS method of quantitative angiography. Procedural success rate was 100%, and there were no major complications. The minimum cross-sectional area of the lesion increased from 0.8 +/- 0.5 mm2 to 3.1 +/- 1.7 mm2 immediately after dilation. Percent area stenosis decreased from 89% +/- 7% to 62% +/- 13%. Six (24%) of 25 lesions developed late physiologically significant restenosis, defined as greater than 15 mm Hg translesional pressure gradient, and 10 of 25 had angiographic restenosis, defined as 50% area stenosis by quantitative angiography. The loss in minimum cross-sectional area of the lesion at late follow-up was related significantly to the minimum cross-sectional area (r = 0.67; p < 0.001) and percent area stenosis (r = 0.62; p < 0.01) immediately after angioplasty and the gain in minimum area (r = 0.62; p < 0.01) or loss in percent area stenosis (0.51%; p = 0.02) during the procedure.(ABSTRACT TRUNCATED AT 250 WORDS)