Background: Although early vascular remodeling of transplant coronary arteries has been reported after cardiac transplantation, the impact of long-term vascular changes on cumulative luminal loss still remains unclear. Methods: In 60 cardiac transplant recipients, serial intravascular ultrasound was performed at 1 month, 1 year, and 3 years after transplantation. At the same levels of 1-month minimal lumen area (MLA), serial changes in external elastic membrane (EEM), intima, and lumen areas were assessed. We also performed quantitative volumetric analysis in order to compare the changes of intima, plaque, and lumen volumes. Results: There was a significant decrease in MLA in the early phase between 1 month and 1 year (11.8짹3.7 mm² vs. 9.9짹3.1 mm², p<0.001, Figure 1), followed by subsequent MLA loss in the late phase between 1 and 3 years (9.9짹3.1 mm² vs. 9.0짹3.5 mm², p=0.013). Although intimal area continued to increase in both early and late phase, significant reduction in EEM area was limited within the early phase, not extended to the late phase. The rates of plaque gain (0.93짹1.55 mm²/year vs. 0.36짹0.95 mm²/year, p=0.043) and EEM shrinkage (-1.16짹2.95 mm²/year vs. -0.15짹1.25 mm²/year, p=0.025) was much greater in the early phase vs. late. The reduction of EEM area in the early phase correlated with early MLA loss (r=0.849, p<0.001) as well as overall MLA loss over 3 years (r=0.608, p<0.001). On volumetric analysis, the trend of volume change was similar to the area changes (Figure 2). Conclusion: Constrictive remodeling was remarkable in the early phase within 1 year and contributed to the lumen loss after cardiac transplantation. Plaque progression also affected the lumen loss over 3 years, while attenuated in the late phase.