A cardiac device in which heart rate variability is computed in order to detect changes indicative of cardiac ischemia. In the case where the device is a pacemaker, the device may alter its pacing mode to limit the rate at which paces are delivered when ischemia is detected. Examples of such pacing mode alterations include discontinuing of rate-adaptive pacing, modification of the responsiveness of the rate-adaptive algorithm, or the decreasing of the maximum allowable pacing rate.