Chemotherapy-associated cardiotoxicity can present as a spectrum from arrhythmia to acute congestive heart failure. Unlike anthracyclines, proteasome inhibitors - for example, bortezomib - are not notorious for causing cardiotoxicity in absence of pre-existing cardiac dysfunction or without concomitant use of other cardiotoxic agents. We describe a 66-year-old woman with end-stage renal disease who developed acute dyspnea hours after a third treatment with bortezomib for IgG kappa myeloma. The Naranjo adverse drug reaction probability scale indicated a probable relationship (score of 5) between bortezomib and acute left ventricular dysfunction. Patients receiving proteasome inhibitors should be closely monitored for evidence of cardiac dysfunction during treatment.