The primary objective of this study is to compare the Apnea- Hypopnea Index in HF patients with concomitant CSA, after 12 weeks of CRT alone to CRT in combination with one night of overdrive pacing. Secondary objectives are to evaluate the effects of a single night of overdrive pacing applied after 12 weeks of CRT vs. CRT alone on breathing events, sleeping events, and neurohormonal markers. An additional secondary objective of the study is to compare the efficacy of CRT in HF patients with concomitant CSA to HF patients without concomitant CSA.