The English literature contains 101 reported cases of cardiac fistula following penetrating thoracic trauma. We describe an additional 10 cases seen during a 7 year period. Six patients had ventricular septal defects, another a ventricular septal defect together with a ventriculo-atrial defect, two patients had aorta--right ventricular fistulous and the final patient, a right coronary artery--right atrial fistula. This series demonstrates several interesting features. First, the mode of clinical presentation in four of the 10 patients was remarkable, because despite severe cardiac injury they initially had neither symptoms nor signs of cardiac decompensation. Second, only two of the seven patients hospitalized immediately after the injury presented with cardiac murmurs suggestive of cardiac fistula formation, whereas the remaining five exhibited cardiac murmurs 1 to 21 days after initial cardiovascular examination. Third, concomitant traumatic valvular lesions occurred frequently (five of 10 cases) but usually were not clinically detectable because of the similarity and dominance of the fistulous murmur. Fourth, it was confirmed that the type of cardiac fistula occurring most commonly following penetrating cardiac trauma was a ventricular septal defect and that conservative management of small ventricular septal defects is compatible with a prolonged asymptomatic course. Finally, attention is drawn to the frequent association of aortic incompetence with aorta--right heart fistulas and the tendency for these fistulas to produce congestive cardiac failure.