Patients with dilated cardiomyopathy (DCM) often have autoantibodies against cardiac antigens including the M2 muscarinic acetylcholine receptor (M2R). To elucidate the role of autoimmunity against M2R in disease development, we induced an immune response against M2R by adoptive transfer into Rag2–/– mice of splenocytes from M2R–/– mice immunized with a recombinant M2R protein. T lymphocytes transiently infiltrated the heart in recipient mice followed by morphological changes in cardiomyocytes. These mice produced IgG antibodies against M2R, which bound to cardiomyocytes in vivo and decreased the amplitude of calcium signals in isolated rat cardiomyocytes in vitro. Recipient mice showed increased heart weights associated with increased intraventricular diameter, decreased systolic function, and increased action potential duration, which are characteristics of DCM. Our results suggest that myocarditis and DCM associated with the presence of anti-M2R antibodies are autoimmune diseases with a risk of progressing to the terminal stage. Our mouse model will be useful in the analysis of the molecular mechanisms of disease progression and the development of new therapies for DCM.