A medical device system for delivering electrical stimulation therapy to a heart of a patient, the system comprising: a first implantable medical device configured to be implanted in a first chamber of the heart 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 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 ; if the value of the first determined parameter passed the first threshold , communicate a first indication to the medical device ; and if the value of the first determined parameter has not passed the first threshold , 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 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 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 ; if the value of the first determined parameter passed the first threshold , communicate a first indication to the medical device ; and if the value of the first determined parameter has not passed the first threshold , not communicating the first indication to the medical device compare a value of a first determined parameter to a first threshold ; if the value of the first determined parameter passed the first threshold , communicate a first indication to the medical device ; and if the value of the first determined parameter has not passed the first threshold , 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 . <EOS>