Objective To assess the benefits of coronary collateral circulation on myocardial perfusion, viability and function in patients with total occlusion of a single coronary artery using the Tc-99m-sestamibi SPECT and F-18-fluorodeoxyglucose PET. Methods 164 Consecutive patients were included who underwent coronary angiography results exhibited total occlusion of a single coronary artery and received Tc-99m-MIBI SPECT and F-18-FDG PET within 90 days of angiography. Myocardial perfusion and viability in patients with collateral circulation and those without it were compared. Long-term follow-up was performed through a review of patient clinical records. Results Collateral circulation was present in 56 patients (34%) and absent in 108 patients (66%). The total perfusion defect size in patients with collateral circulation decreased when compared to those without (30% +/- 13% to 35% +/- 14%, P < .05). The myocardial viability was 22% +/- 12% in patients with collateral circulation, and 12% +/- 9% in those without (P < .001). The left ventricular ejection fraction was higher, and the end-diastolic and end-systolic left ventricular volumes were lower in patients with collateral circulation (39% +/- 11%, 138 +/- 66, 89 +/- 57) compared to patients without collateral circulation (31% +/- 9%, 177 +/- 55, 125 +/- 48, all P < .001, respectively). Multi-factor logistic regression identified that concerning the variables of sex, age, viable myocardium, collateral circulation, treatment type and others, only treatment type was significantly associated with therapeutic effects (OR 3.872, 95% CI 1.915-7.830, P < .001). Conclusion Collateral circulation can preserve resting myocardial blood perfusion and myocardial viability, and help maintain the function of the left ventricular myocardium. The appropriate treatment strategy will have a substantial impact on the therapeutic outcome.