This case report illustrates challenging aspects of diagnosis and treatment of isolated sarcoid heart disease (SHD) and the role of cardiovascular magnetic resonance (CMR) imaging. Here, we present a previously healthy 45-year-old man, who was admitted with pericardial effusion and symptoms of acute heart failure. CMR followed by targeted left ventricular endomyocardial biopsy (EMB) revealed the diagnosis of isolated SHD. The combined use of CMR and EMB was crucial in diagnosing SHD. Furthermore, this case report demonstrates the value of CMR for monitoring response to therapy and lesion healing.