Myocarditis is an inflammatory disease of the heart muscle that can be triggered by various causes, including viruses, autoimmune response, molecular mimicry and exposure to immune-stimulating drugs or vaccines. Most cases of myocarditis heal, and cardiac dysfunction, if present, recovers; however, selected forms may require targeted therapy to improve outcomes. We herein review five conditions presenting with or mimicking myocarditis that require targeted diagnostic approaches, including endomyocardial biopsy, and/or targeted treatments. Giant cell myocarditis is an intense and unresolving inflammation of the heart, characterised by rapid progression, significant arrhythmias, heart failure and shock, that is unlikely to resolve without immunosuppression therapy.