A case of systemic lupus erythematosus (SLE) associated with fever, heart failure, and left ventricular (LV) aneurysm is reported. A diagnosis of SLE was suspected owing to the presence of active lymphocytic myocarditis and fibrinous endocarditis at LV endomyocardial biopsy and was confirmed by identification of 4 of the 11 criteria proposed by the American Rheumatism Association for the definition of SLE. A 2-month period of steroid therapy was followed by a remarkable recovery of LV function and progression of endomyocarditis to a healed phase at control LV biopsy. The LV aneurysm disappeared, likely because thrombosis occurred as a result of the hypercoagulable state accompanying the presence of anticardiolipin antibodies. This is the first reported case of LV aneurysm induced by SLE and is a rare clinicohistologic documentation of the effectiveness of steroid treatment on lupus endomyocarditis.