Single coronary artery (SCA) is a rare congenital coronary anomaly in which all three major coronary arteries arise from a single aortic sinus. We present a unique case of a 59-year-old female who underwent coronary computed tomography angiography (CTA) for evaluation of new-onset ventricular ectopics and epigastric discomfort. Imaging revealed a solitary coronary artery arising from the right sinus of Valsalva, giving rise to the right coronary artery (RCA), left anterior descending artery (LAD), left circumflex artery (LCx), and a prominent ramus intermedius. The LAD had a benign prepulmonic course, while the LCx followed a retroaortic route. Notably, the ramus intermedius coursed between the aorta and pulmonary artery (interarterial), and was the dominant vessel supplying the lateral wall of the left ventricle due to diminutive obtuse marginal branches. This configuration is a previously undescribed variant diverging from the classic R-III Lipton classification and represents a potentially malignant anomaly. Recognition of such atypical and hemodynamically significant variants is crucial for clinical risk stratification and interventional planning.

Keywords: Single Coronary Artery; Lipton Classification Variant; Interarterial Ramus; Coronary CT Angiography; Malignant Coronary Anomaly; R-III Deviation