Objective: Cardiac involvement has been documented in a number of primary muscular dystrophies, but the mechanisms responsible for the pathogenesis of cardiomyopathies in these disorders are still poorly understood. We investigated the contractile function of myocardial preparations in a mouse model for X-linked dilated cardiomyopathy. Methods: Isolated papillary muscle preparations of dystrophin knockout-mice (C57BL/mdx, 20–30 g, 14–20 weeks) were investigated and compared to age-matched wild-type muscles (C57BL/10). Force of contraction was elicited by electrical stimulation (1–4 Hz) and measured isometrically under physiological conditions (37°C, [Ca2+]o 1.8 mM).Results: Force-frequency relationship was strongly negative in wild-type papillary muscles and, less pronounced, in mdx muscles (BL/10: Fmax 3,27±0.55 [1 Hz] vs 1.56±0.24 mN/mm2 [4 Hz], mdx: Fmax 0.26±0.04 [1 Hz] vs 0.20±0.03 mN/mm2 [4 Hz]). Force production was up to 10-fold greater in wild-type muscles at all stimulation freqencies. Contraction kinetics were not significantly different between the two mouse species.Conclusions: In an X-linked dilated cardiomyopathy mutant mouse model, contractile myocardial force, but not contraction kinetics, is severely reduced.