Objective: Dystrophin provides mechanical reinforcement to the membranes of myocytes. Dystrophin abnormalities are known to cause cardiomyopathy and skeletal muscle disorders; however, the pathogenesis of these abnormalities remains unclear. Dystrophin-deficient skeletal muscle is vulnerable to stresses such as stretch and hypo-osmotic shock. We investigated whether the myocardium of dystrophin-deficient (mdx) mice shows increased vulnerability to acute pressure overload in vivo. Methods and results: Abdominal aortic banding was performed in 12-week-old mdx and control mice. The aortic pressure was measured by cannulation of the right carotid artery at the time of sacrifice. Systolic pressures in mdx mice at 0, 1, 2, 7 and 14 days after aortic banding were 100±11, 119±7, 123±4, 134±11 and 130±10 mmHg, respectively. Microscopic analysis revealed focal lesions in the left ventricular wall in banded mdx mice. These lesions consisted of damaged myocytes and inflammatory cells, and also of fibrosis at a late stage. Similar lesions were not observed in non-banded or banded control mice. The proportion of areas of lesions to total left ventricular area increased over time: 1.0±0.6% in mdx mice without aortic banding (sham, n=6), and 1.7±1.4% 1 day (n=6, vs. sham, NS), 2.6±1.9% 2 days (n=7, vs. sham, P<0.05), 6.3±6.5% 7 days (n=13, vs. sham, P<0.05) and 9.9±8.3% 14 days after aortic banding (n=15, vs. sham, P<0.01). Furthermore, linear regression analysis revealed a significant correlation between percentage of lesion area and systolic pressure in mdx mice (P<0.05). Conclusion: Dystrophin-deficient myocardium is more vulnerable than normal myocardium to pressure overload in vivo. This result has two clinical implications: (1) the patients with dystrophynopathy, such as the Duchenne and the Becker types of muscular dystrophy and X-linked type of dilated cardiomyopathy, who develop arterial hypertension should be treated aggressively, and (2) they should avoid stresses that elevate blood pressure.