Monitoring of intracoronary ST segment during PCI, up to the end of the procedure will be performed according to flow chart . The technique has been described elsewhere (22). Briefly, the proximal end of the wire chosen for recanalization will be used as a unipolar derivation which substitutes the V5 leads on precordial ECG. ST resolution will be monitored during the procedure and ECG acquisition will be done at baseline, after effective thrombus aspiration, after intracoronary drugs administration and at the end of the procedure. Each ECG will be quantitatively assessed. Lack of resolution will be defined as a ST elevation resolution of < 30%. Partial resolution will be considered a ST resolution ≥30% but <70%. Furthermore times needed to obtain full or partial ST resolution will be recorded. Anginal pain at starting and at each time points will be assessed.