This case illustrates how important it is to monitor a patient who is being treated for heart failure and also receiving sleep ventilation therapy.  As a component of cardiac optimization, CRT may be associated with significant increases in a patient’s LVEF, and several studies have shown that with this change in cardiac function, a patient’s CSA will change.  For example, as shown in the study by Kara,^[1] if CRT is stopped for just one night, there will be an increase in central apnea; restarting the CRT will decrease the CSA again.  Other studies have shown the same results for the AHI, a decrease in AHI following initiation of CRT.^[2,3]  This effect may have a latency, perhaps as long as >6 months, before ascertaining whether a patient’s sleep apnea improves with the CRT.