Background:Patients at high bleeding risk would benefit from a shorter dual antiplatelet therapy after PCI. Compared to first-generation devices, the design of newer generation drug-eluting stents may facilitate more rapid anatomical and functional healing of stented vessel based on thinner stent platforms, biodegradable/biocompatible polymers and rapid drug elution.Methods and Results:Forty-four non-diabetic patients with acute coronary syndrome (ACS) and culprit lesion in the LAD were randomized to receive either biodegradable polymer sirolimus-eluting stent (BP-SES) or durable polymer zotarolimus-eluting stent (DP-ZES). Neointimal strut coverage was examined using optical coherence tomography, and vasodilator response on invasive thermodilution-derived coronary flow reserve (CFR) at 3-month follow-up. The primary endpoints were percent uncovered struts and CFR. A total of 425 cross-sections (4,897 struts) were analyzed in the BP-SES group, and 425 cross-sections (5,467 struts) in the DP-ZES group. The percent uncovered struts was lower in the BP-SES group compared with the DP-ZES group, both at strut level (3.9% vs. 8.9%, respectively, P<0.001), and stent level (3.9±3.2% vs. 8.9±6.9%, respectively, P=0.019). No significant difference was found between the 2 groups regarding CFR (3.0±1.3 vs. 3.2±1.0, respectively, P>0.05).Conclusions:In non-diabetic patients with ACS, BP-SES provided slightly better stent strut coverage at 3 months compared with DP-ZES, but neither stent was fully covered. No difference in vasodilator response was seen. (Circ J 2015; 79: 360–367)