A method and medical device for monitoring cardiac function in a patient that includes a plurality of electrodes to deliver cardiac pacing therapy, and a processor configured to determine a pacing threshold in response to initial delivery of the pacing therapy, determine whether there is a change in the pacing threshold during initial delivery of the pacing therapy, adjust a delivery parameter of the pacing therapy in response to determining the change in the pacing threshold during initial delivery of the pacing therapy, determine whether there is an increase in the pacing threshold during delivery of the adjusted pacing therapy, and determine hypokalemia in response to the increase in the pacing threshold during delivery of the adjusted pacing therapy being present.