The efficacy of PTCA was evaluated in several subgroups of patients. Of special clinical interest were the comparisons between subgroups of patients with multivessel disease vs 1-vessel disease, unstable angina vs stable angina, older age vs younger age, and female sex vs male sex. As a prerequisite for such comparisons, baseline characteristics of patients in the subgroups were examined. Compared with the subgroup with 1-vessel CAD, the subgroup with multivessel CAD had more elderly patients (age 65 years and older) and more of these patients had previous MI or CABG. PTCA was more often unsuccessful in patients with multivessel CAD because of inability to pass the catheter across the lesion. The subgroup of women tended to be older than men, and more women had severe and unstable angina, although fewer had multivessel CAD, previous MI or previous CABG. The PTCA success rate was 5% lower in women because of a greater frequency of inability to pass the lesion. Compared with younger patients, older patients had a higher prevalence of severe angina, multivessel CAD and lesions with larger diameters. The older patients had a 5% lower PTCA success rate, once again because of a greater frequency of inability to pass the lesion. The learning experience with PTCA was measured by the overall success rate as well as by the rate of ability to pass the lesion and the rate of dilating it once it was passed. These rates improved significantly by the investigators' case accumulations and independently by calendar year. Multivariate prediction of crossing the lesion and of overall success showed that favorable lesion characteristics and increasing physician experience were more important than the patient characteristics just discussed, although both female sex and multivessel CAD remained significant independent risk factors.