Percutaneous coronary intervention (PCI) in thrombus-containing lesions may be associated with microembolization and microcirculatory dysfunction which may limit myocardial recovery. Objective was to determine the predictors of improvement of left ventricular regional function after PCI in thrombus-containing lesions in patients with acute coronary syndromes (ACS). Thirty-five consecutive patients (52 ± 9 years, 29 males) with ST-elevation (21pts) and non-ST elevation myocardial infarction (14pts) for the first time were included. All patients had angiographic evidence of intraluminal thrombus and regional motion asynergy on echocardiography. All patients had successful PCI; the X-sizer thrombectomy catheter system was used in 10 pts. The thrombus scoring system, thrombolysis in myocardial infarction (TIMI) flow grade, corrected TIMI frame count (cTFC), tissue myocardial perfusion grading (TMP) and myocardial dye intensity (by measuring gray scale level of myocardial blush in cinifilms) were assessed before and after the procedure. The left ventricular wall motion score index (WMSI) was determined before and 6 months after intervention by echocardiography. Improved regional left ventricular function at follow-up (Fu) was defined as WMSI reduction > 0.3 (the mean WMSI decrease in all patients).Results : Patients were divided into two groups: 20 pts with improved WMSI (the WMSI at baseline was=1.73±0.46 in the improved group vs 1.45±0.4 in non-improved group, p=0.06, and was1.26±0.41 in the improved group vs 1.58±0.40 non-improved group at 6ms Fu) and 15 pts without. Baseline clinical and angiographic data were similar in both groups. There was no difference in postprocedural TIMI 3 flow and cTFC. Forward step wise logistic regression revealed that TMP (p=0.007) and use of X-sizer (p=0.03) are two independent predictors for WMSI improvement in this model (R square = 0.64). WMSI at Fu showed significant correlation with the difference between the thrombus score before and after intervention (r=0.42, p=0.012) and myocardial dye intensity (r = -0.65, p<0.001) Conclusions: In thrombus-containing lesions, tissue myocardial perfusion grading and pretreatment with a thrombectomy device may predict short-term improvement of regional left ventricular function.