Here we report our experiences on the construction of a skeletal muscle pumping chamber (SMPC) of a biomechanical cardiac assist device made in situ with the Latissimus Dorsi (LD) of sheep. Main results are : i) its feasibility, ii) its long-standing continuous contractile activity. From the end of the three-week conditioning the SMPC is activated 24 h a day at 30 Hz with a duty cycle of 125 msec on 1 sec off. In 3-month stimulated LD the proportion of fatigue-resistant type 1 fiber substantially increases (up to loo%, compared to the 10-20% before conditioning). Isomyosins' analyses confirme that the fast types are eliminated leaving only the type 1 isoform.