Higher grades of collateral circulation limit the extent of myocardial ischemia observed during balloon inflation in patients with single vessel coronary disease undergoing coronary angioplasty. However, the grade of collateral filling during sudden coronary occlusion varies from patient to patient. To assess which characteristics may predict a high grade of collateral filling, baseline clinical and angiographic variables were correlated with the grade of filling during coronary occlusion in 67 patients (whose angina ranged from 1 week to 36 months in duration) undergoing left anterior descending or right coronary artery angioplasty. A second contralateral arterial catheter was used to assess the collateral filling that reached the vessel dilated before and during transient total occlusion by the angioplasty balloon. Thirty-six patients had a proximal stenotic lesion ranging in severity from 65 to 99%. On a 0 to 3 scale, mean collateral filling grade before inflation was 0.4 versus 1.8 during inflation (p = 0.001). All 19 patients with 95 to 99% stenosis had at least grade 2 collateral filling during inflation. In contrast, 18 of 21 patients with less than or equal to 80% stenosis had only grade 0 or 1 collateral filling during inflation. There were significant positive correlations between collateral grade during inflation and 1) baseline lesion severity (r = 0.76), 2) baseline collateral filling grade (r = 0.50), and 3) vessel dilated. There was no relation between collateral filling during inflation and age, gender, risk factors, duration of angina or proximal versus distal location of the lesion. Lesion severity was the only independent variable associated with collateral filling grade.(ABSTRACT TRUNCATED AT 250 WORDS)