Devices and methods for improving device therapy such as cardiac resynchronization therapy (CRT) by determining a desired value for a device parameter are described. An ambulatory medical device can be configured to detect a heart sound signal and generate one or more heart sound metrics, detect a characteristic indicative of cannon waves, and determine a desired value for a device parameter, such as a timing parameter which can be used to control the delivery of CRT pacing to various heart chambers. The desired device parameter value can be determined using the heart sound metrics and the characteristic indicative of the cannon waves. The ambulatory medical device can program stimulation using the desired device parameter value, and deliver the programmed stimulations to one or more target sites to achieve desired therapeutic effects.