Transcatheter embolisation was performed in a six year old child with a large haemodynamically significant arteriovenous fistula between the left coronary artery and right ventricle. The fistula seemed to fill via a single large septal branch of the left anterior descending coronary artery. This was occluded distally with a detachable balloon backed up by a proximal coil. After this the flow through the fistula was considerably reduced but it still filled via a small diagonal branch that had not been noted previously. This branch was subsequently occluded in its most distal part by a coaxial catheter technique and a single microcoil. Complete occlusion of the fistula was produced and there were no complications.