Heart failure occurs when the heart can no longer pump blood adequately. CRT appears to improve this condition by electrically stimulating the heart to achieve better coordinated blood-pumping contractions. Most HF patients also appear to be at high risk for potentially fatal derangements in the heart’s electrical activity. Should this occur, ICD devices may be used to shock the heart back into a normal electrical rhythm, potentially averting death, but ICDs do nothing the rest of the time to reduce HF symptoms. The principal question addressed by COMPANION was whether adding CRT with or without ICD treatment to the medical management of HF patients with a wide QRS not only improved functional measures but also reduced hospitalization rates and all-cause mortality (Bristow et al., 2004). Previous studies, including the MIRACLE trial (2002), demonstrated that CRT alone improved the New York Heart Association (NYHA) functional class, exercise duration, and quality of life of HF patients who did not require an ICD or traditional pacemaker, but they did not have sufficient power to discriminate a mortality benefit (Abraham, Fisher, et al., 2002). In patients who require ICD implantation mainly for secondary prevention of sudden cardiac death and who also have HF, an ICD has been shown to significantly reduce mortality but does not appear to improve HF symptoms. Two trials—CONTAK-CD (Higgins, Hummel, et al., 2003) and MIRACLE-ICD (Young, Abraham, et al., 2003)—examined whether adding CRT to the ICD in these patients improved outcomes. Both had fairly short follow-up periods and insufficient power to discriminate differences in mortality or hospitalization, but they did demonstrate improved patient NYHA functional status.