CT
Axial C+ arterial phase
3D VRT
Both the right coronary artery (black arrow) and left main stem (white arrow) arise from the right coronary sinus (from separate ostia). The left main stem has a pre-pulmonic course, passing anterior to the right ventricular outflow tract.
The left main stem bifurcates into the left anterior descending artery (blue arrow) and circumflex artery (green arrow).