A 38-year-old man with a history of bronchial asthma developed marked eosinophilia, mononeuritis multiplex and transient pulmonary infiltration. Pathological findings from the lung and nerve biopsy were helpful in determining the diagnosis as allergic granulomatosis and angiitis (AGA). Echocardiogram indicated dilation of the left ventricle with impaired systolic contraction. Coronary arteriography demonstrated significant stenosis only in the peripheral segment of the circumflex artery. After 1 year of corticosteroid therapy, echocardiogram revealed improvement of left ventricular contractility evaluated by ejection fraction (from 28% to 67%). To our knowledge, no previous reports have described amelioration of severe cardiac lesions during long-term steroid treatment in patients with AGA.