<p>Cardiac allograft vasculopathy (CAV) is a major cause of mortality after heart transplantation, characterized by intimal proliferation-induced coronary stenosis. The first year post-transplantation represents a critical period for CAV development, with most intimal proliferation occurring during this timeframe. This study aimed to investigate the temporal changes in lipid content and its relationship with intimal proliferation during the first year after heart transplantation. Serial three-vessel near-infrared spectroscopy intravascular ultrasound (NIRS-IVUS) and optical coherence tomography (OCT) were performed in 15 heart transplant recipients (38 coronary arteries) at 2 months (baseline) and 12 months (follow-up) following heart transplantation. From baseline to follow-up, the highest lipid-core burden index within a 4 mm segment (maxLCBI_4mm) significantly decreased (median: 78.0 [IQR: 6.75 to 196] to 27.5 [IQR: 0 to 122], <i>p</i> = 0.008), while %intimal volume (intimal volume/vessel volume × 100) increased (median: 16.2% [IQR: 15.3 to 17.5] to 18.3% [IQR: 15.3 to 20.1], <i>p</i> = 0.006). Receiver operating characteristics (ROC) analysis identified a maxLCBI_4mm cut-off of 124 for detecting OCT-assessed fibroatheroma (area under the ROC curve: 0.942, <i>p</i> &lt; 0.001). In vessels with donor-transmitted fibroatheroma (maxLCBI_4mm ≥ 124 at baseline), higher baseline maxLCBI_4mm correlated with both more significant subsequent reduction in maxLCBI_4mm (r² = 0.482, <i>p</i> = 0.003) and more extensive intimal volume proliferation (r² = 0.321, <i>p</i> = 0.022). Coronary artery lipid content generally decreased during the first year after heart transplantation. In vessels with donor-transmitted fibroatheroma, higher baseline lipid burden correlated with substantial lipid reduction and subsequent intimal volume proliferation.</p>