Latissimus dorsi pedicle grafts (LDPGs) were wrapped around the heart in eight dogs. In four dogs, the LDPGs were stimulated chronically; the remaining four dogs served as unstimulated controls. Right-sided cardiac filling pressures were normal in all dogs when measured 4 months after graft application. Mean tension generated by the viable LDPGs was 153 +/- 49.9 g. LDPGs contracting in synchrony with the heart did not increase cardiac output. In one dog, the aortic pressure changed from 140/100 to 155/85 mm Hg during synchronous contraction of the LDPG. Three dogs were placed on cardiopulmonary bypass, and their hearts were placed in fibrillation. The LDPGs were then stimulated at a burst frequency of 85 Hz and contracted vigorously. Under these conditions, the left ventricular pressure increased by an average of 15 mm Hg with each LDPG contraction; however, the mean aortic pressure was virtually unchanged. Left ventricular and aortic pressures of 125/20 and 125/65 mm Hg, respectively, could be obtained with manual compression of the fibrillating heart. This study indicates that although LDPGs can be made to contract chronically and in synchrony with the heart, they do not necessarily augment left ventricular performance.