PURPOSE: Autonomic symptoms during seizures may provide information on seizure onset zone. We investigated whether changes in heart rate (HR) and HR variability (HRV) occur during subclinical electrographic seizure patterns, and whether these have a localising/lateralising value. METHODS: EEG and ECG recordings of pharmacoresistant epilepsy patients who underwent intracranial video-EEG telemetry were reviewed. Ultra-short-term HRV expressed as standard deviation of the mean before, during and after the subclinical seizure pattern was determined in 10s epochs. Statistics were done with a linear mixed regression model. Values are expressed as mean+/-SD. RESULTS: 26 patients (38+/-10 years, 13 of either gender) have been included; 7 patients with temporal lobe epilepsy (TLE) of either side as well as 7 (right-sided lesion) and 5 patients (left-sided lesion) with frontal lobe epilepsy (FLE). A total of 74 subclinical events (2-3 per patients) were analysed. Pooled data for HR only weakly increased during and after the subclinical pattern with a mean HR of 80+/-10 bpm before to 82+/-11 bpm during (p=0.03) and 81+/-10 bpm after subclinical patterns (p=0.06). HR was higher in patients with left TLE as compared to right TLE (p=0.001). In FLE patients only, the change in HR was correlated with the spatial extent of electrographic pattern localised (p=0.03). Mean HRV did not change during or after subclinical patterns. HRV was; however, lower in TLE patients with left-sided subclinical patterns as compared to right-sided patterns (pre-event HRV left 13+/-6 ms, right 34+/-16 ms). CONCLUSIONS: Our data revealed only minimal changes in autonomic cardiac function during highly localised electrographic seizure patterns and this had no localising/lateralising value.