Clinical cardiomyopathy is an uncommon complication of systemic lupus erythematosus (SLE) and intracavitary thrombosis is rare. We describe a patient with active SLE who developed rapidly progressive cardiomyopathy, the fatal course of which was complicated by an intracavitary thrombus. Repeat cardiac echography studies and the endomyocardial biopsy proved to be helpful in diagnosing the lupus myocarditis and aided the regulation of therapy. Furthermore, the patient presented an acute suppurative thyroiditis never before described, to our knowledge, in SLE.