The occurrence of no-reflow phenomenon after recanalization of the infarct related artery in acute myocardial infarction is described in up to 40% of cases. This event is associated with a worse prognosis at follow up and an unfavourable left ventricular remodelling. Two main pathogenetic mechanisms cause no-reflow: distal embolization and ischemia-reperfusion injury. Microembolization, which may be well prevented by a mechanic approach (device-based), play of course an important role in the no-reflow during primary percutaneous coronary intervention (primary PCI), however ischemia reperfusion injury is also independent of microemboli, indeed it occurs in the animal model after ligation of a non atherosclerotic coronary. Thrombus aspiration assisted primary intervention achieves complete resolution of the ST segment in 60% only of patients, whereas results of filter based studies have been substantially negative. A recent meta-analysis confirmed that thrombus aspiration improves microvascular perfusion, whereas filters do not.