COMPANION was an RCT with three treatment arms, designed to evaluate the efficacy of CRT and CRT-D in patients with HF (NYHA class III or IV), cardiomyopathy (with a left ventricular ejection fraction < 35 percent), delayed ventricular conduction (QRS >120 msec), and no specific indication for an ICD or pacemaker. A total of 1,520 patients were randomized. Patients were assigned in a 1:2:2 ratio to receive optimal pharmacological therapy (OPT), OPT + CRT, or OPT + CRT-D. Follow-up duration was until the primary end point (which averaged about 16 months for those who reached an end point during the two years of the study). The primary-efficacy end point was a composite of either death from any cause or hospitalization from any cause.