Background: Few data are available about the follow-up patency of side branches after currently used drug-eluting stent (DES) implantation in the setting of primary stenting for acute ST-elevation myocardial infarction (STEMI). Methods: From the prospective randomized study of ZEST-AMI trial comparing the outcomes of three DES comprising sirolimus-eluting stent (SES), paclitaxel-eluting stent (PES), and zotarolimus-eluting stent (ZES) in primary stenting for 328 patients with acute STEMI, 111 side branches (SB) with  2.0mm in diameter from 96 infarct-related lesions were selected for qualitative angiographic analysis at post-procedure and follow-up. Results: Forty-seven percent of SB was located in diagonal branch. SB balloon angioplasty was performed in 10% of lesions. From 111 SB, Impaired TIMI flow  grade 2 occurred in 32% of SES, 33% of PES, and 36% of ZES (p=0.152). However, from 75 SB receiving 9-month angiography, impaired TIMI flow was not significantly changed from 8.0% (6 SB) at post-procedure 9.3% (7 SB) at follow-up. Conclusion: During primary stenting with current DES, impairment of SB flow was not uncommon regardless of the DES type. At serial angiography, SB flow was not significantly changed over 9-month period.