Clozapine is an alternative antipsychotic medication used to control symptoms of schizophrenia and to reduce risks of suicidal behavior in patients who did not adequately respond to standard medication. Due to severe side effects including cardiomyopathy and myocarditis its clinical use is limited.A 31-year-old man of east European descent presented to the emergency medical department with fatigue, shortness of breath and chest pain. Due to a schizoaffective disorder he was treated with clozapine and lithium. Echocardiography revealed severely impaired left ventricular systolic function. After exclusion of coronary artery disease by coronary angiography an endomyocardial biopsy was performed according to the guidelines. This confirmed the clinically suspected toxic cardiomyopathy. Therefore, antipsychotic treatment was immediately changed and state of the art heart failure medication was started resulting in a clear improvement of left ventricular function.In patients treated with clozapine or lithium and clinical signs of heart failure, toxic cardiomyopathy should be considered.