A technique is presented for transplantation of the heart and left lung en bloc in the dog. In contrast to the erratic respiratory pattern that occurs in subprimate animals after total cardiopulmonary denervation, preservation of innervation to the native right lung results in a normal respiratory pattern in the dog and has allowed survival of one animal for 68 days. This model is proposed as potentially suitable for physiologic and immunologic studies of cardiopulmonary transplantation in the dog.