The study is a prospective cohort study conducted in Tianjin Chest Hospital, China. Patients with saphenous vein graft disease after coronary artery bypass graft, and planning for receiving percutaneous coronary intervention after virtual histology intravascular ultrasound will be enrolled between May 2017 and April 2019. These subjects will be followed up at 1, 6 and 12 months post-operation of PCI to assess the short-term and long-term effect.