OCT (optical coherency tomography) imaging will be performed at the same time as the patient's regularly scheduled surveillance cardiac catheterization (1 month and 12 months after heart transplant). OCT imaging will be performed with the commercially available second-generation frequency domain Ilumien Optis (St. Jude Medical, St. Paul, MN). The OCT catheter (Dragonfly Duo) will be advanced over a 0.014-inch coronary guide wire into the middle segments of all three main arteries (left anterior descending, left circumflex and right coronary artery) and imaging will be performed by automated pullback with a length 45 mm, with pullback speed 25 mm/sec in high resolution mode (10 frames /mm). OCT examination will be performed after administration of 200-300 μg of intracoronary nitroglycerin and simultaneous injection of 14 ml of contrast agent to each artery by power injector through the guiding catheter. OCT data will be used for 3-D vessel reconstruction done by the fusion with routine angiography performed in two projections at least 60 degree apart.