Balloon dilatation and stenting of thrombotic lesions remains a challenge for coronary intervention due to insufficient reduction of thrombus and the risk of abrupt vessel closure, distal embolization and no reflow. Mechanical thrombus removing devices (TRD) have been introduced as accessory tools for the extraction or dissolution of coronary thrombi.The X-SIZER thrombectomy system operates by cutting through the thrombus and aspirating the destroyed clot debris whereas the Acolysis Ultrasund Thrombolysis system works by disintigrating thrombi into minute subcapillary size debris utilizing low frequency high energy ultrasound. Following clinical evaluation (including ECG and laboratory testing) and diagnosic coronary arteriography , 60 pts with acute ischemic syndromes and angiographic evidence of thrombus were randomly chosen to be pretreated either with the X-SIZER or the Acolysis or proceeded directly to PCI without prior use of a TRD. The X-SIZER group included 23 pts (21 males, 2 females, mean age 51 + 10 yrs ) with STEMI in 19 pts and UAP in 4 pts. The Acolysis group included 15 pts with STEMI (14 males, 1 female, mean age 51+10 yrs). The Control group included 22 pts with STEMI (18 males, 4 females , mean age 50+9 yrs ). All pts were subjected to cardiac catheterization within a mean period of 1+0.5 hrs from admission and a mean period of 3.5+3 hrs from the onset of chest pains . All pts received periprocedural IIb/IIIa platelet receptors blockers. Compared to prethrombectomy , X-SIZER-treated vessels showed a significant increase in TIMI flow grade (2.65 + 0.67 vs 0.6 + 0.88, p < 0.005 ), decrease in Diameter Stenosis (53.3+16.6 vs 87.9 + 19.5 , p < 0.005) achieving an Acute Luminal Gain by X-SIZER alone of 1.15 + 0.57 mm (41 % of total luminal gain) . The Thrombus Burden was 36.8+21.1 mm2 which decreased to 5.1 + 8 mm2 after X-SIZER alone with a Thrombus Burden Reduction of 86 + 15 % , (P< 0.005). Compared to prethrombolysis , Acolysis-treated vessels showed a significant increase in TIMI flow grade (1.67 vs 0 , p < 0.05), decrease in diameter stenosis (72 + 22 vs 99 + 2 , p < 0.005) with an Acute Luminal Gain by Acolysis alone of 1.04 + 0.8 mm ( 35 % of total luminal gain) . The Thrombus Burden was 31 + 4 mm2 which decreased to 12 + 11 mm2 after Acolysis alone with a Thrombus Burden Reduction of 57 + 37 %, (p< 0.005). Comparing X-SIZER with Acolysis treated vessels immediately after the procedures, the X-SIZER was more successful than acolysis in increasing TIMI flow (2.65 + 0.67 vs 1.67 + 1, P: 0.01), decreasing diameter stenosis (53 + 17 vs 72 + 22, P: 0.009) and thrombus burden reduction (86 + 15 vs 57 + 37 %, P: 0.009). Compared to the control group both X-SIZER & Acolysis groups after final adjunctive PCI showed a significantly higher final TIMI flow grade (2.57 + 0.6 vs 2.95 + 0.2 vs 2.93 + 0.26 , P: 0.008 ). A nonsignificant difference was found between all 3 groups in Total Luminal Gain of (2.88 + 1 vs 2.78 + 0.85 vs 2.95 + 0.6 mm , p: 0.85). X-SIZER treated patietns with STEMI had a significantly increased successful S-T segment resolution which was observed in 88% of X-SIZER treated patients, while only in 67 % of the Acolysis group and 53 % of the control group, P: 0.05 and lower incident of Distal Embolization and No Reflow (9% vs 28% vs 27%, P : 0.04) and MACE (4% vs 20% vs 14%, P : 0.004). In conclusion, the use of thrombus removing devices is a real addition to the interventional therapy of acute ischemic syndromes with thrombus rich lesions through cutting and aspiration or disintigration into subcapillary size debris as an adjunctive treatment prior to balloon dilatation or stenting. The X-SIZER catheter system seems more effective than Acolysis Ultrasound thrombolysis in improving free coronary flow and microvascular reperfusion with less incidence of complications.