Pulmonary infections can be a major complication of heart transplantation. Bacterial pneumonia has decreased markedly in the last few years among heart recipients receiving cyclosporine as immunosuppressive therapy. Fungal infections of the lung can cause serious problems in the compromised condition of these patients, with several deaths attributed to Aspergillus and Candida. To our knowledge, however, there has been no report of pulmonary mucormycosis in heart transplant recipients. We describe, therefore, a heart transplant patient with insulin-dependent diabetes mellitus who developed serious cavitary pulmonary mucormycosis. Diagnosis was made by transbronchial biopsy, and treatment required both prolonged administration of amphotericin B and surgical resection to effect a cure. The diagnostic problems and therapeutic considerations associated with pulmonary mucormycosis are discussed.