A system to monitor heart sounds. The system comprises an implantable heart sound sensor configured to produce an electrical signal representative of at least one heart sound, an implantable posture sensor operable to produce an electrical signal representative of a patient's posture, and a controller circuit. The controller circuit is configured to determine a patient posture, measure at least one heart sound in correspondence with at least one corresponding patient posture, adjust the heart sound measurement by using the corresponding determined patient posture to reduce or remove variation in the heart sound measurement due to patient posture, detect a change in the adjusted heart sound measurement, and provide an indication of congestive heart failure to a user or an automated process in response to the detected change.