The effect of radiographically graded coronary collateral vessels on regional myocardial blood flow was evaluated with intracoronary injection of xenon-1233 at rest and during contrast agent-induced coronary hyperemia in 24 patients with coronary artery disease. Eleven patients had no coronary collateral vessels demonstrated radiologically, whereas 13 had such vessels. In 7 of the 13 these were high grade and noncompromised, whereas in 6 they were of lesser grade. Regional myocardial blood flow at rest in patients with and without collateral channels was similar and increased during hyperemia. However, the increase in flow was significantly greater in the patients with high grade noncompromised collateral vessels than in those with lesser grade collateral vessels (80 +/- 16 versus 31 +/- 9 plercent, p < 0.05). To evaluate the functional significance of the high grade noncompromised collateral vessels against that of vessels of lesser grade, various indexes of global and regional ventricular function were compared in the 13 patients in the present study, as well as in 24 patients whose collateral vessels had been subjected to similar grading systems in previous studies of regional myocardial blood flow. There were no significant differences in degree of regional asynergy, ejection fraction or left ventricular end-diastolic pressure between the patients with high and lower grades of collateral vessels. Thus, high grade noncompromised collateral vessels do not appear to have a beneficial effect on resting left ventricular function despite their enhanced vasoldilatory reserve.