A 60-year-old woman was admitted with acute heart failure and was diagnosed as having primary systemic AL amyloidosis with cardiac involvement by endomyocardial biopsy. Electrophoresis revealed an IgG-lambda monoclonal component and amyloidosis was evident in the gastric and rectal mucosa. Her cardiac function at diagnosis was poor, including an ejection fraction of 59% and IVS of 19 mm, and serum cardiac troponin T (cTnT) was elevated (0.12 ng/ml). She was treated with melphalan-dexamethasone (Mel-Dex) therapy once a month. After more than a year, cardiac function and performance status were maintained, with decreasing levels of cTnT, indicating that Mel-Dex represents a feasible and effective therapeutic option for patients with AL amyloidosis with cardiac dysfunction.