Adult polyglucosan body disease (APBD) is a rare genetic disorder, inherited in an autosomal recessive mode. The disease is caused by mutations of the gene coding for the glycogen-branching enzyme, which is essential for branching of polyglucose chains in the normal glycogen molecule. The age of clinical manifestation of the disease mostly is between 40 and 60 years and its course is slowly progressive. Characteristic globular deposits (polyglucosan bodies, PGB) can be detected in biopsies of skin and skeletal muscle as well as in the peripheral and central nervous system. Biochemically, PGBs consist of poorly branched glycogen molecules with abnormally long polysaccharide chains. We report the case of a 50-year-old female patient with APBD who suffered from neurological symptoms such as spastic tetraparesis, urinary incontinence, hypesthesia and dementia. She died unexpectedly of cardiac failure. At autopsy a severe cardiomyopathy with abundant PGBs in the heart muscle fibres could be proven as the cause of death. This observation shows that in addition to the known deposition of PGBs in nervous system and skeletal muscle, an involvement of the heart has to be considered in APBD as well.