Clinical trials with carfilzomib have indicated a low but reproducible incidence of cardiovascular and renal toxicities. Among 60 consecutive myeloma patients treated with carfilzomib-based regimens who were thoroughly evaluated for cardiovascular risk factors, 12% (95% confidence interval, 3.8%-20%) experienced a reversible reduction of left ventricular ejection fraction (LVEF) by ≥20%, an objective measure of cardiac dysfunction. The incidence of LVEF reduction was 5% at 3 months, 8% at 6 months, 10% at 12 months, and 12% at 15 months, whereas the respective carfilzomib discontinuation rate unrelated to toxicity was 17%, 35%, 41%, and 49%. The presence of any previously known cardiovascular disease was associated with an increased incidence of cardiac events (23.5% vs 7%; = .07), but there was no association with the dose of carfilzomib or the duration of infusion. Re-treatment with carfilzomib at lower doses was possible. Carfilzomib was commonly associated with a transient reduction of estimated glomerular filtration rate (eGFR) but also improved renal function in 55% of patients with baseline eGFR <60 mL/min/1.73 m. Further investigation is needed to elucidate the underlying mechanisms of carfilzomib-related cardiorenal toxicity.