Abstract: An implantable medical device includes a sensor and a T-wave analyzer. The sensor is implantable within the body of a patient to sense electrical cardiac activity and provide an indication of T-wave alternans within the heart of the patient. The T-wave analyzer is responsive to the sensor, and evaluates cardiac risk based on comparison of the indication of T-wave alternans to a predetermined criterion. The T-wave analyzer may form part of a microprocessor, a digital signal processor, or combination of both. The device may include a pacing generator that applies increased rate pacing stimuli to the heart to facilitate sensing of the T-wave alternans by the sensor. The device also may incorporate a memory that stores the T-wave alternans indication provided by the sensor, e.g., over a number of heartbeats. In addition, the device may be equipped to provide an alert to the patient or a physician in the event the processor generates the indication of cardiac risk.