Two cases of coronary artery right ventricular fistula were diagnosed during the yearly check-up of 38 of the 66 cardiac transplant patients of the Montreal Heart Institute between September 1982 and April 1989. In one case, the fistula involved the right anterior ventricular branch of the right coronary artery and in the other case, a septal branch of the left anterior descending artery. Histological examination of the biopsy fragments obtained before diagnosis of the fistula showed the presence of small calibre arteries, which was not the case in 10 control transplant patients. A review of the literature indicates that the risks of endomyocardial biopsy are minimal (less than or equal to 0.5%). However, the possibility of a coronary artery right ventricular fistula should be added to the list of known complications. The resulting shunt is negligible and has no haemodynamic consequences.