All patient will receive intravenous administration of abciximab prior to PCI. After wire crossing, thrombus aspiration will be performed. The device will removed outside the body, flushed with saline and subsequently reintroduced in the culprit vessel beyond the occlusion site and intracoronary drugs will be selectively administered. At this stage the patient will be randomized either to intracoronary Adenosine (80 mcg as fast bolus followed by 2 mg given in 33cc of saline in 2 minutes as slow bolus), nitroprusside (60 mcg as fast bolus followed by 100 mcg given in 33cc of 5% glucose in 2 minutes as slow bolus) or placebo (33 cc of heparinized saline given in 2 minutes as slow bolus). Due to the short half-life of both drugs we have chosen a bolus plus infusion regimen in order to allow a more sustained effect of the two drugs on the microcirculation. The safety and efficacy of this drug regimen has been tested in a small pilot study in our catheterization laboratory. We have compared the two drugs regimens to traditional single bolus administration of adenosine for the evaluation of fractional flow reserve (FFR) in ten patients (5 for adenosine and 5 for nitroprusside) undergoing pressure wire evaluation of an intermediate stenosis. We found similar FFR in both groups but more prolonged dilatation of the microcirculation compared to group of traditional single bolus adenosine administration (data not shown).