Timeline of the study. In this retrospective study of a clinical practice change, sirolimus group consisted of patients undergoing IVUS examination within 1 year after conversion from CNI to sirolimus. CNI group comprised those who were maintained on CNI and underwent IVUS examinations during the study period. The first (baseline) and the last (follow-up) IVUS examinations were used for analysis. Study patients were subclassified into three groups according to the time interval between HTx and study inclusion (baseline IVUS): early (≤2 years), intermediate (between 3 to 5 years), or late (≥6 years). CNI indicates calcineurin inhibitor; HTx, heart transplantation; and IVUS, intravascular ultrasound.