Summary:An infant who received haploidentical BM for severe combined immunodeficiency (SCID) developed acute, reversible complete heart block in association with an exacerbation of GVHD. Respiratory distress and myocardial dysfunction were also seen with this and previous GVHD exacerbations. The patient had not received chemotherapy or radiation prior to BMT. The complete heart block resolved after 1 week of intensive immunosuppression. The association of complete heart block with GVHD is important because the heart block is potentially reversible with prompt, aggressive control of the GVHD. Keywords: cardiac; heart block; arrhythmia; graftversus-host disease; bone marrow transplantation Graft-versus-host disease is a major cause of morbidity and mortality after bone marrow transplantation. GVHD manifestations are predominantly limited to the skin, gastrointestinal tract, and liver. 1 However, severe GVHD is associated with a marked release of cytokines ('cytokine storm') 2 that may result in more widespread organ involvement. Cardiac involvement during acute or chronic GVHD has been reported to be infrequent, mild and generally asymptomatic. 3,4 We report the second case of complete atrioventricular block occurring in association with GVHD. A case of complete heart block has been reported in a patient with SCID who received an haploidentical parental marrow transplant. The patient had acute GVHD of the skin, liver and gut which was treated with high-dose steroids and monoclonal antibody. He had recurrent symptoms and signs of chronic GVHD and was maintained on low-dose steroids. Skin and liver biopsies were consistent with chronic GVHD. The patient developed complete heart block at day +97 and required a pacemaker. A myocardial biopsy showed interstitial edema, focal mononuclear cell infiltrate, and individual fiber degeneration. The lymphohistiocytic infiltrate resembled that from the skin biopsy. The patient Correspondence: Dr A Gilman, Pediatric Hematology/Oncology, The Children's Mercy Hospital, 2401 Gillham Road, Kansas City, MO 64108, USA Received 14 March 1997; accepted 14 July 1997 died 1 month later and autopsy results showed similar infiltrates with foci of necrosis and scarring present in the atrioventricular node, bundle of His and myocardium. No evidence of viral infection was found on the premortem biopsy specimen or at autopsy. 5 The patient in our report was treated with intensive immunosuppression, had reversal of his complete heart block, and remains well. Case reportThe patient was diagnosed with SCID when he presented at 4 months of age with Pneumocystis carinii pneumonia and failure to thrive. He had severe pneumonia and required a high-frequency ventilator and nitric oxide for 2 weeks. He had no clinical evidence of cardiac dysfunction. Immunophenotyping showed a lack of T lymphocytes and NK cells, and the presence of B lymphocytes. He received haploidentical T cell-depleted bone marrow from his father. T cell depletion was performed with OKT3 antibody and rabbit complement, which resulted...