AIM: This study was conducted as a feasibility pilot for the Prediction of Risk In Syncope using ECG characteristics (PRISE) study. The secondary aim was to determine whether heart rate variability (HRV) characteristics may be useful to distinguish low and high-risk syncope patients. METHODS: Adult patients presenting to the emergency department (ED) with syncope over a one-month period underwent a 5-minute 12-lead ECG. Study patients were assigned high, medium or low-risk status according to the ED\'s existing syncope guidelines as well as one of four likely diagnostic categories. ECG signals from all patients were then analysed and time domain HRV characteristics were derived using WelchAllyn\'s Cardioperfect interpretation software. A control group of patients was also recruited. RESULTS: Over a 4-week period in July 2007, 32 patients were recruited into the study group and 23 into the control group. ECG tracings of five study group patients were not suitable for analysis. According to the ED\'s existing syncope guidelines there were nine low-risk, 12 medium-risk and six high-risk patients with diagnostic categories as follows: postural hypotension, five; vasovagal, 16; cardiac, five and other, one. Patients with cardiac syncope had greater mean values for all HRV characteristics except NN number and NN minimum; however, with overlapping confidence intervals. Low-risk patients were more likely to be younger than medium and high-risk patients. No HRV parameters showed any significant differences. CONCLUSIONS: Measuring HRV in the acute ED setting is feasible. If patients with cardiac and neurocardiogenic syncope have different HRV characteristics then it could be useful to determine a patient\'s underlying cause of syncope in the ED, which would allow earlier decision-making.