The performance of 7F guiding catheters for percutaneous transluminal coronary angioplasty (PTCA) was investigated in 300 patients. A total of 233 patients had single-vessel PTCA and 67 had multivessel PTCA. Angioplasty was attempted for 371 lesions (141 [38%] in the left anterior descending, 124 [33%] in the right coronary artery, and 95 [26%] in the left circumflex coronary artery or their branches; 10 [3%] in a bypass graft, and one in the left main stem). The mean degree of stenosis was 86 +/- 11% (range 60% to 100%). The monorail technique was used in 83%, and balloon-on-a-wire devices were used in 6% of cases. The balloon sizes varied between 2.0 and 4.25 mm. There was a 98% technical success rate for the 325 nontotal lesions. Five could not be crossed with the wire. Exchange to an 8F guiding catheter was done in four cases (1.2%) and yielded success in two of them. In 46 occlusions the success rate was 72%. Nine were failures due to an inability to cross the wire, another two were balloon failures, and in two cases the residual stenosis was greater than 50%. The mean residual stenosis of successful cases was 24 +/- 18%. Overall, the primary success rate was 95%. The complications were: in-hospital death in five patients (1.7%); infarction in 12 (4%); emergency bypass surgery in one; and significant inguinal hematoma in five (1.7%). Coronary angioplasty through 7F guiding catheters yields a high success rate with less coronary wedging and a smaller puncture hole.