Autoimmune encephalitis can be associated with other autoimmune disorders, but the concurrent presence of autoimmune encephalitis and autoimmune myocarditis is uncommon. A man in his 80s with type 2 diabetes mellitus, hypertension and hypothyroidism presented with altered mental status for 8 months. He was previously diagnosed with myasthenia gravis, but therapy was discontinued due to infection. On presentation, he was wheelchair-bound with disorientation, proximal weakness, hyporeflexia and bradykinesia. MRI brain showed atrophy, and cerebrospinal fluid analysis revealed mildly elevated protein (58.8 mg/dL) without pleocytosis. Despite treatment for urinary tract infection and septic encephalopathy, his sensorium did not improve. A diagnosis of possible autoimmune encephalitis was considered, though antibody studies were negative. Whole-body Positron Emission Tomography - Computerized Tomography (PET-CT) ruled out malignancy and showed global hypokinesia, while echocardiography showed severe left ventricular systolic dysfunction. Positive acetylcholine receptor antibody led to intravenous immunoglobulin therapy, which improved his sensorium and cardiac dysfunction suggesting a positive association.