Drug-eluting stents (DES) have been extremely successful in reducing restenosis and the need for repeat revascularization procedures in patients who undergo PCI. The potential increased incidence of late stent thrombosis prompted cardiologists to prolong the use of dual anti-platelet therapy after the one year duration recommended by the recent ESC guidelines. However, while the premise that the cardiologists should put all their patients on dual clopidogrel-aspirin regimen for life sounds the easy way, it is an unrealistic goal because of the potential increase of bleeding complications and of the healthcare cost increase. The recent possibility to monitor aspirin with bedside assays offers a real opportunity to compare in good aspirin responder patients the two strategies: aspirin-clopidogrel regimen versus mono-aspirin regimen and to respond to the key question: can the investigators switch from dual to single antiplatelet therapy after six months in good aspirin responder patients ? Study National, multicenter, randomised prospective open group comparison of dual clopidogrel-ASA versus single ASA regimen after six months, in good ASA responder patients treated with DES (name: XIENCE) implantation.