1. A medical device, comprising: a sensor adapted to detect a candidate heart beat; a cardiac data collection module operatively coupled to said sensor, said cardiac data collection module adapted to obtain a time series of fiducial time markers for candidate heart beats; a constraint-modifying heart beat validation module operatively coupled to said sensor and said cardiac data collection module, said constraint-modifying heart beat validation module adapted to identify valid heart beats from said candidate heart beats by subjecting a plurality of said candidate heart beats to at least one beat validity test, said at least one beat validity test comprising at least one interbeat interval test applied to a candidate heart beat interval derived from a candidate heart beat and at least one prior heart beat, and accept as valid heart beats the candidate heart beats that pass said at least one beat validity test, wherein a constraint defining said pass is modified after the most recent prior valid heart beat that is greater than a constraint modification time threshold; a seizure detection module configured to detect an epileptic seizure using a seizure detection algorithm based on said accepted valid heart beats; and at least one responsive action module adapted to perform at least one action based upon an epileptic seizure detected by said seizure detection module, the responsive action module selected from the group consisting of: a neurostimulation delivery module; a warning module; and a modified constraint logging module.