An apparatus for monitoring a patient's blood glucose level. The apparatus includes an implantable medical device having a controller and an implantable heart sounds sensor configured to transmit signals to the controller of the implantable medical device. The controller is configured to determine if a patient is hypoglycemic or hyperglycemic based on the signals from the heart sounds sensor. A method is also disclosed that includes sensing the patient's heart sounds, determining the amplitude of the S2 heart sound, determining the length of the interval from the S1 heart sound to the S2.sub.max heart sound, determining the length of the interval from the S1 heart sound to the S2.sub.end heart sound, and determining the patient's blood glucose status based on the patient's heart sounds.