Introduction: Determining the relationship of no-refl ow phenomenon (NRP) in patients (pts) with ST segment elevation myocardial infarction (STEMI) and primary percutaneous transluminal coronary angioplasty (PTCA) with age, gender, cardiovascular risk factors, ECG location of STEMI, culprit coronary artery, angiographic characteristics of obstructive lesions. Methods: 81 pts with STEMI and primary-PTCA, performed within 3 hours aft er the onset of the symptoms, were evaluated for NRP at pts with TIMI 3 score postPTCA. NRP was diagnosed on the culprit coronary artery by Doppler transthoracic echocardiography. NRP was defined through the systolic reverse fl ow with peak velocity ≥ 10 cm/s, duration ≥ 60 ms and diastolic deceleration time less than 600 ms. Pts were divided in 4 groups according to age and gender: men less than 40 years 28 (35%) (M < 40 years), female less than 40 years 4 (5%) (F < 40 years), men over 40 years 36 (44%) (M > 40 years), female over 40 years 13 (16%) (F > 40 years). Statistics performed with SPSS 20, with comparisons between groups, bivariate correlations and logistic regression. Statistical significance was at p < 0.05. Results: NRP was found in 26 pts (32%), 10 M < 40 years (36%), 10 M > 40 years (28%) and 6 F > 40 years (46%), significantly more often in F > 40 years than in M > 40 years (p = 0.02). NRP has been signifi cantly correlated in M < 40 years with dyslipidemia (p = 0.005), procoagulant conditions (p = 0.01) and thrombus lesions of culprit coronary artery (p = 0.001). In M > 40years, NRP was significantly correlated with anterior ECG localization of STEMI (p =0.001), obstruction of left anterior descending artery (LAD) (p = 0.001), thrombosis on atherosclerotic plaque (p = 0.004), arterial hypertension (p = 0.007) and in F > 40years with coronary obstruction by thrombus on atherosclerotic plaque (p = 0.01). Conclusions: No-reflow phenomenon documented by TTE Doppler criteria on the flow of the culprit coronary artery occurs frequently, in descending order in female over 40 years, men less than 40 and men over 40 years. No-reflow phenomenon was significantly correlated in men less than 40 years with thrombosis as culprit lesion, dyslipidemia, procoagulant conditions, in those over 40 years with anterior ECG location of STEMI, LAD occlusion, thrombus on atherosclerotic plaque as culprit lesions and arterial hypertension. In women over 40 years no-reflow phenomenon was significantly correlated with thrombosis on atherosclerotic plaque as culprit lesion.