Techniques are provided for detecting dilated cardiomyopathy within a patient using a pacemaker or other implantable medical device. Briefly, values representative of QT duration and QT dispersion are detected within the patient and then the risk of dilated cardiomyopathy is evaluated based on the values of QT duration and QT dispersion. In one particular example, the implanted device calculates an index representative of the extent to which individual QT duration and QT dispersion values deviate from a daily mean. The device then compares the index against a threshold indicative of a substantial likelihood of the presence of dilated cardiomyopathy within the patient. Additional techniques described herein relate to distinguishing dilated cardiomyopathy from heart failure within patients that may have one or both conditions.