The use of abciximab during percutaneous coronary angioplasty (PTCA) in patients with unstable angina (UA) prevents the postintervention enzyme surge and improves clinical outcomes, possibly by improving microcirculatory function. The aim of this quantitative myocardial blush grade (MBG) study was to verify whether abciximab improves postintervention microcirculation in patients with UA. This prospective randomized open-label study involved 140 UA patients scheduled to undergo PTCA of the target coronary lesion: 140 patients were randomized to receive either abciximab during PTCA (group 1, 70 patients) or conventional treatment without GP IIb/IIIa inhibitor (group 2, 70 patients). The exclusion criteria included above normal CK-MB levels. MBG was calculated by means of quantitative software that evaluates video intensity in a given region of interest: assuming that greater peak video intensity reflects a larger myocardial blood volume, a perfusion scale of 1-6 points (poor to optimal) was devised. The groups were homogeneous in terms of their demographic, procedural, and angiographic characteristics. Stents were used in 98% of the patients in both groups. The MBG score significantly increased in group 1 from 3.04 +/- 2.17 to 3.71 +/- 2.02 (P = 0.045) and slightly decreased in group 2 from 3.13 +/- 2.07 to 2.93 +/- 2.03 (P = 0.42). Consequently, group 1 showed a significantly greater postintervention MBG score (3.71 +/- 2.02 vs. 2.93 +/- 2.03; P = 0.022) and had a significantly greater MBG score change (P = 0.025). The results of this randomized study show that the administration of abciximab prevents microcirculatory impairment in patients undergoing angioplasty for acute coronary syndromes.