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 whether there is a change in the pacing threshold during initial delivery of the pacing therapy, determine whether there is a decrease in the pacing threshold during delivery of the adjusted pacing therapy, and determine hyperkalemia in response to the decrease in the pacing threshold during delivery of the adjusted pacing therapy being present.