Background-Intracardiac pressures in heart failure (HF) have been measured in patients while supine in the hospital but change at home with posture and activity. The optimal level of chronic ambulatory pressure is unknown. This analysis compared chronic intracardiac pressures to later HF events and sought a threshold above which higher pressures conferred worse outcomes. Methods and Results-Median pressures were measured every 24 hours from continuous 8-minute segments for 6 months after implantation of hemodynamic monitors in 261 patients with New York Heart Association class III-IV HF in the Chronicle Offers Management to Patients with Advanced Signs and Symptoms of Heart Failure Study. Baseline and chronic daily medians of estimated pulmonary artery diastolic, right ventricular systolic, and right ventricular end-diastolic pressures were compared with HF event rate. The group median for chronic 24-hour estimated pulmonary artery diastolic pressure was 28 mm Hg (excluding 7 days before and after events). Despite weight-guided management, events occurred in 100 of 261 (38%) patients. Event risk increased progressively with higher chronic 24-hour estimated pulmonary artery diastolic pressure, from 20% at 18 mm Hg to 34% at 25 mm Hg and 56% at 30 mm Hg, with similar relations for right ventricular pressures. Among patients with baseline day median estimated pulmonary artery diastolic pressures of ≥ 25 mm Hg, event risk was 1.10/6 mo when they remained chronically ≥25 mm Hg, but risk fell to 0.47 when 24-hour pressures declined to <25 mm Hg for more than half of the days. Conclusions-Despite current management, many patients with advanced HF live on a plateau of high filling pressures from which later events occur. This risk is progressively higher with higher chronic ambulatory pressures. It is not known whether more targeted intervention could maintain lower chronic ambulatory pressures and better outcomes. © 2010 American Heart Association, Inc.