A 67 year old woman was admitted for assessment of asymptomatic aortic stenosis. A large left atrial myxoma was demonstrated by 2D and M mode echocardiography. Coronary angiography was performed as part of the investigation of the aortic stenosis and showed that the tumour depended on the right coronary artery for its blood supply. Careful frame-by-frame study showed the presence of a true right coronary-left coronary fistula through the tumour. The authors discuss the different clinical presentations of left atrial myxomas and their vascularisation in the rare cases in which it has been described.