Background:Functional ischemic mitral regurgitation (MR) is a common complication of acute MI and is an independent predictor of worse long-term prognosis in patients with acute STEMI treated with primary PCI. Our aim is to detect the impact of collateral circulation to the infarct zone in addition to other clinical and echocardiographic risk factors to the incidence of early ischemic mitral regurgitation (MR) in Egyptian patients presenting with acute STEMI after primary PCI. Subjects and Methods: The study included 144 patients with acute STEMI who underwent primary PCI. The patients were divided into two groups: Group 1: 72 patients with ischemic MR; and Group 2: 72 patients with no MR. All patients were subjected to history, ECG, CKMB, creatinine, PCI and transthoracic echo to assess LV EF% and MR severity. Results: Patients in group I (MR group) were more frequently females, had lower BMI, less B-blocker and ACEI use, had higher LA and LVEDD index, lower LVEF, increased incidence of multi-vessel disease, Rentrop class 3-4, increased incidence of heart failure and in-hospital mortality. We found that female gender, lower BMI, lower EF% and well-developed collateral were independent MR predictors. Based on the independent predictors of MR (gender, BMI, Rentrop class and EF), the cut-off values were 40.5% for LVEF and 28.87 for BMI. With the following scoring system: female gender (1); male (0), BMI < 28.87 (1); BMI >28.87 (0), EF <40.5 % (1); EF > 40.5% (0), and Rentrop class (0.1,2,3). The sensitivity of predictive risk score ≥3 based on the independent predictors of significant MR was 94.4% and the specificity was 52.8%. Conclusion: A predictive risk score ≥3 based on the independent predictors of significant MR (female gender, lower BMI, LVEF%, well-developed collateral supply to the MI region) may be helpful in predicting MR occurrence with high diagnostic accuracy. Keywords: STEMI, primary PCI, ischemic MR, collateral circulation