OBJECTIVES This study investigated the cost effectiveness of early cardiac resynchronization therapy (CRT) implantation among patients with mild heart failure (HF). The differential cost effectiveness between CRT using a defibrillator (CRT-Ds) and CRT using a pacemaker (CRT-P) was also assessed. BACKGROUND Cardiac resynchronization has been shown to be cost effective in New York Heart Association (NYHA) functional classes III/IV but is less studied in class II HF. The incremental costs of early CRT implementation in mild HF compared with the costs potentially avoided because of delaying disease progression to advanced HF are also unknown. Finally, combined biventricular pacing and defibrillator (CRT-D) devices are more expensive than biventricular pacemakers (CRT-P), but the relative cost effectiveness is controversial. METHODS Data from the 5-year follow-up phase of REVERSE (REsynchronization reVErses Remodeling in Systolic Left vEntricular Dysfunction) were used. The economics were evaluated from the U.S. Medicare perspective based on published clinical projections. RESULTS Probabilistic estimates yielded $8,840/quality-adjusted life year (QALY) gained (95% confidence interval [CI]: $6,705 to $10,804/QALY gained) for CRT-ON versus CRT-OFF (i.e., programmed "ON" or "OFF" at pre-specified post implantation timings) and $43,678/QALY gained for CRT-D versus CRT-P (95% CI: $35,164 to $53,589/QALY gained) over the patient-s lifetime. Results were robust to choice of patient subgroup and alterations of 10% to key model parameters. An "early" CRT-D class II strategy totaled $95,292 compared with $91,511 for a "late" implantation. An "early" implant offered on average 1.00 year of additional survival for $3,781, resulting in an ICER of $3,795/LY gained. CONCLUSIONS This study demonstrates CRT cost effectiveness in mild HF. The incremental CRT-D costs are justified by the anticipated benefits, despite increased procurement costs and shorter generator longevities. "Early" CRT-D implants have essential cost parity with "late" implants while increasing the patient-s survival. (C) 2017 by the American College of Cardiology Foundation. Published by Elsevier.