This clinical trial will be a randomized double-blind study focusing on ticagrelor antiplatelet therapy as a means of improving vein graft patency after CABG. Patients will be eligible if they have received at least 1 vein bypass graft at time of surgery. Patients will be randomized to receive either aspirin 81 mg bid or ticagrelor 90 mg bid. The aspirin and ticagrelor medications will be prepared in blinded capsules. Patients recovering from surgery will be eligible for study randomization within the first 5 postoperative days. Treatment will continue for 1 year, at which time patients will undergo a CT coronary angiogram to assess graft patency. Patients will then be invited to continue participating in the trial for 1 more year, and a repeat CT coronary angiogram will be performed at the 2 year postoperative time-point.