We report a method for detecting epileptic or non-epileptic seizures, comprising: receiving a heart rate of a patient; calculating a percentage change of the heart rate in reference to at least one of the patient's maximal heart rate, reserve heart rate, or a resting heart rate; detecting an epileptic seizure if the percentage increase in the heart rate reaches a threshold value; and taking at least one responsive action selected from issuing a warning, delivering a therapy, determining a seizure severity, or logging at least one of a date and time of occurrence of the seizure, its severity, the type of therapy, or its effect, in response to the detection. We also report a medical device system configured to implement the method. We also report a non-transitory computer readable program storage unit encoded with instructions that, when executed by a computer, perform the method.