We describe a case of successful intrauterine treatment with dexamethasone for fetal carditis in a woman with systemic lupus erythematosus. Targeted dual M-mode fetal echocardiogram showed disappearance of pericardial effusion and heart failure with therapy. The maternofetal pair had several of the factors considered a risk for passively transmitted autoimmune carditis. Our case further supports the evidence that dexamethasone could be effective for intrauterine treatment of this clinical situation.