A medical device system (300, 400, 500) for delivering electrical stimulation therapy to a heart (410, 510) of a patient, the system comprising: a first implantable medical device configured to be implanted in a first chamber of the heart (410, 510) and configured to determine one or more parameters; a medical device physically housed separately from and communicatively coupled to the first implantable medical device, the medical device configured to deliver electrical stimulation therapy to the heart (410, 510) of the patient, wherein the first implantable medical device is further configured to: compare a value of a first determined parameter to a first threshold (604, 704b); if the value of the first determined parameter passed the first threshold (604, 704b), communicate a first indication to the medical device; and if the value of the first determined parameter has not passed the first threshold (604, 704b), not communicating the first indication to the medical device wherein after communicating the first indication to the medical device, the first implantable medical device is configured to: compare the value of the first determined parameter to a second threshold, where the second threshold is different from the first threshold; if the value of the first determined parameter passed the second threshold, communicate a second indication to the medical device; and if the value of the first determined parameter has not passed the second threshold, not communicating the second indication to the medical device. a first implantable medical device configured to be implanted in a first chamber of the heart (410, 510) and configured to determine one or more parameters; a medical device physically housed separately from and communicatively coupled to the first implantable medical device, the medical device configured to deliver electrical stimulation therapy to the heart (410, 510) of the patient, wherein the first implantable medical device is further configured to: compare a value of a first determined parameter to a first threshold (604, 704b); if the value of the first determined parameter passed the first threshold (604, 704b), communicate a first indication to the medical device; and if the value of the first determined parameter has not passed the first threshold (604, 704b), not communicating the first indication to the medical device compare a value of a first determined parameter to a first threshold (604, 704b); if the value of the first determined parameter passed the first threshold (604, 704b), communicate a first indication to the medical device; and if the value of the first determined parameter has not passed the first threshold (604, 704b), not communicating the first indication to the medical device wherein after communicating the first indication to the medical device, the first implantable medical device is configured to: compare the value of the first determined parameter to a second threshold, where the second threshold is different from the first threshold; if the value of the first determined parameter passed the second threshold, communicate a second indication to the medical device; and if the value of the first determined parameter has not passed the second threshold, not communicating the second indication to the medical device. compare the value of the first determined parameter to a second threshold, where the second threshold is different from the first threshold; if the value of the first determined parameter passed the second threshold, communicate a second indication to the medical device; and if the value of the first determined parameter has not passed the second threshold, not communicating the second indication to the medical device.