Abstract Background and aim: In ST elevation myocardial infarction (STEMI), intracoronary thrombolysis after primary percutaneous coronary intervention (PPCI) was found to improve microvascular perfusion, yet without improvement in left ventricular (LV) remodeling. Our study aimed to find out possible effect on LV longitudinal function. Check for updates [2] and LV function [3-7]. In addition to the metabolic derangement of reperfusion injury [8,9], both proximal embolization [10,11] and microvascular in-situ thrombosis [12] play role in microvascular damage. Methods and results: 102 anterior STEMI patients eligible for PPCI were divided into: Alteplase group (53 patients; received intracoronary 0.3 mg/kg alteplase after PPCI) and control group (49 patients; treated with PPCI only). LV longitudinal function was assessed using tissue Doppler imaging (to measure mean S' and maximum Q-S' time difference) and speckle tracking (to measure global longitudinal strain (GLS)) 48 hours and 6 months after PPCI. In alteplase group, epicardial (p value < 0.001 for corrected TIMI frame count) and myocardial perfusion (p value for myocardial blush grade 0.03) were significantly higher. GLS and LV synchrony were better in alteplase group both at 48 hours (p value 0.02 and < 0.001 respectively) and at 6 months (p value < 0.001 for each). No difference in bleeding rates was noted between groups. Conclusion: Adjunctive low-dose alteplase infusion after PPCI improves microvascular perfusion and LV longitudinal function without increasing bleeding risk.