The article presented a clinical case of 8-year follow-up of a patient with a relatively beneficial course of pulmonary sarcoidosis and intrathoracic lymph nodes and with gradually progressing myocardial injury. A specific feature of the case was that the patient had monoclonal gammopathy, which is extremely rarely reported. Morphological signs of paraproteinemic hemoblastosis and amyloidosis were not observed. The article considered a whole complex of studies, which is required for diagnosing cardiac sarcoidosis in a specific patient and addressed the issue of monoclonal gammopathy origination.