Introduction: Several reports have stated cardiac involvement in possible female carriers of Duchenne (DMD) and Becker (BMD) muscular dystrophy. As carriers can now be positively identified by DNA analysis it has become possible to study LV function in DNA-proven and obligatory D/BMD carriers. Methods: BMD and DMD carriers in the age of 18-60 years, registered at the dept. of Human Genetics in Leiden were invited to participate in the study. Carrier status was established by pedigree or DNA analysis. Women with hypertension, coronary disease, valve dysfunction, or severe co-morbidity were excluded. Left ventricular (LV) function and wall motion was assessed by M-mode and 2-D transthoracic echocardiography. Results: A total of 129 women were included: 85 DMD and 44 BMD carriers. Their mean age was 37 +/- 10 years. Mean LV end diastolic diameter (LVED) was 50 +/- 5 mm, mean shortening fraction (SF) was 37 +/- 7%, and mean E-point septal separation (EPSS) was 5 +/- 2 mm. None had more than mild mitral, aortic or tricuspid regurgitation. Fourteen DMD and 4 BMD carriers had LV abnormalities. LV dilatation (LVED > 57 mm) was observed in 8 DMD, reduced SF (< 27%) in 1 BMD and 3 DMD, increased EPSS (> 8 mm) in 1 BMD and 6 DMD, and 4 DMD had regional wall motion abnormalities. Diastolic dysfunction (E/A ratio < 1) was noted in 2 BMD and 2 DMD. Six DMD carriers were considered to have dilated cardiomyopathy. Conclusion: LV dysfunction is more frequently seen in DMD as compared to BMD carriers. Although most carriers appear to have normal LV function, manifest cardiomyopathy is seen in 7% of DMD carriers.