<p>This study aimed to analyze and quantify the influence of cardiac positional variation on the amplitude of coronary artery movement and its potential dosimetric impact during breast carcinoma radiotherapy. 121 4DCT datasets from female patients with left-sided breast cancer were collected. The left anterior descending (LAD) coronary artery and its three segments (proximal, middle, and distal) were delineated to determine its movement amplitude. Subsequently, the dosimetric impact due to the LAD motion-inclusion effect was evaluated. All three LAD segments exhibited different displacement magnitude, with the highest magnitude of 15.9 <i>±</i> 12.6&#xa0;mm for the distal segment in the right direction. The displacement of LAD resulted in an average reduction of -4.30% (range: -18.29% to 32.53%) and − 5.36% (range: -13.72% to 8.04%) in the mean dose and V15 Gy for the whole LAD, respectively. All three segments exhibited different dosimetric variation in dose parameters, with the average mean dose variation found to be -3.00%, 8.10%, and − 9.10% for the proximal, middle, and distal segments, respectively. A significant correlation was found between age and the proximal LAD displacement, however, not with its dosimetric parameters. The study demonstrates that cardio-respiratory motion can significantly affects the displacement amplitude and dose parameters of LAD segments. The three LAD segments exhibited different displacement magnitudes, with the distal segment moving the most. The middle segment was susceptible to higher radiation exposure than other segments, warranting segment-specific anisotropic expansion margins around the LAD to mitigate motion-induced dose uncertainties during treatment planning.</p>