Background A left coronary artery with atypical origin originating from the right coronary sinus with interarterial course was found in a 68-year-old man, who had been referred to the hemodynamics unit for ventricular extrasystoles, observed on ECG, which raised suspicions of suspect coronary heart disease. Methods Atypical origin was observed on a coronary angiography, and interarterial course was confirmed with a coronary CT. Results The left coronary artery is observed arising from the right aortic sinus, in an ostium separated by 5 mm to the left of the right ostium. The left coronary trunk was 28 mm long, with eccentric calcium plaque in the distal third of the coronary trunk, and 50% stenosis. The right coronary artery was of normal caliber. Conclusions Atypical origin of the left coronary artery is a rare condition, normally associated with sudden death.