Background Long-term clinical and hemodynamic benefits of dynamic cardiomyoplasty (DC) have been reported. However, no information is available about long-term morphological changes in the wrapped latissimus dorsi (LD) muscle in humans.Methods and Results The LD muscle flap was evaluated by magnetic resonance imaging (MRI) in 13 patients submitted to dynamic cardiomyoplasty for treatment of severe dilated cardiomyopathy.Eight patients were studied 15 days after the surgery (group 1) and 5 patients were studied from 24 to 52 months after the surgical procedure at the time of the cardiomyostimulator replacement (group 2). In the interim, LD was stimulated with burst of 6 pulses (duration, 185 milliseconds; burst frequency, 30 Hz) synchronized to every cardiac contraction, with a maximum of 100 LD contractions per minute. Images were acquired on a GE Sigma 1.5-T system (echo time, 25 milliseconds; repetition time, R-R x 2; slice thickness, 8 mm). The thickness of the LD decreased from 19.6+-7.3 mm for group 1 to 7.6+-0.8 mm for group 2 (P<.01). In addition, the signal intensity of the LD was compared with that of thoracic skeletal muscle and was found to be significantly increased in group 2 (2.19+-0.42) compared with group 1 (1.04+-0.07, P<.001). The signal intensity for group 2 on the T1-weighted images was similar to that of subcutaneous fat in those images.Conclusions Morphological changes in the wrapped LD muscle consistent with fatty degeneration occur after DC and can be detected by MRI.Further studies will be necessary to demonstrate the clinical significance of such LD muscle flap changes. (Circulation. 1994;90(part 2):II-102-II-106.)