Immunoglobulin light chain (AL) amyloidosis is a systemic disorder caused by depositions of insoluble amyloid fibrils that are composed of fragments of monoclonal light chains produced by abnormal plasma cells. The prognosis is reported to be poor; median survival time (MST) is 1-2 years overall, and is 6 months in patients with cardiac involvement. We here report the treatment outcomes of 24 patients with AL amyloidosis at our hospital between January 2008 and December 2012, including 11 patients with cardiac involvement. MST from the diagnosis was significantly shorter (9.8 months) in patients with cardiac involvement. Of these, patients who achieved a decrease of B-type natriuretic peptide (BNP) to <200 pg/mL after treatment survived longer than patients who did not (MST: not reached vs. 6.1 months; p = 0.003, log-rank test). The median time to decrease BNP to <200 pg/mL was 6.3 months. The decline of BNP to 200 pg/mL or less during treatment predicts longer survival in patients with cardiac AL amyloidosis.