A 56-year-old woman with mixed connective tissue disease, who was on maintenance immunosuppression, developed asymptomatic left ventricular dysfunction, ventricular arrhythmia, and high troponin I. Heart catheterization showed normal coronaries and biopsy-proven, virus-negative lymphocytic myocarditis. A biopsy-guided immunosuppression upgrade effectively treated autoimmune myocarditis, which resulted in ventricular function recovery, resolution of arrhythmia, and of troponin release. (Level of Difficulty: Advanced.)