The case of an asymptomatic patient with prolapsing left atrial myxoma, in whom preoperative coronary angiography revealed a rare coronary artery anatomy in the absence of atherosclerotic obstructive disease, is presented. There was a type IV dual left anterior descending (LAD) artery with intraseptal course of the right aortic sinus-connected (long) LAD artery and an ectopic left circumflex artery originating from the right aortic sinus and having a retroaortic course. The patient underwent successful surgical excision of the mass which was confirmed by histology to be cardiac myxoma. This particular coronary artery anatomy has only been described once, and this is the first reported case of its combination with cardiac myxoma. This report highlights the importance of differentiating between the possible courses of such ectopic coronary arteries. The angiographic signs which enabled differentiation of the intraseptal course of the long LAD artery from the malignant interarterial course with which it is frequently confused are presented.