Patients with de novo, coronary bifurcation lesions with jailed side branches after successful drug-eluting stent implantation at the main branches will be prospectively and consecutively enrolled. Control group patients will be selected from the database.

Jailed side branches need to have an ostial stenosis >50%, vessel size >2 mm, vessel length >40 mm and lesion length <10 mm by visual estimation.

Study procedure Coronary stenting of the main branch should be performed with standard interventional techniques using drug-eluting stents. In the FFR group, pressure measurement would be performed using a 0.014 inch pressure guide wire (PressureWire, Radi Medical Systems, Uppsala, Sweden)Lesions with an FFR <0.75 are considered to have functionally significant stenosis and side branch balloon dilatation is allowed only for these lesions. It is recommended to use a smaller balloon than the side branch vessel diameter. After kissing balloon inflation, FFR will be measured again at the same site and further intervention is only recommended when FFR was <0.75 after kissing balloon dilatation. In the conventional group, the decision to treat the side branch lesion and the method of intervention are all up to the operators’ discretion.