A screening procedure and apparatus enables those at risk of cardiac arrhythmia to be identified. The procedure utilises a blood flow detector (12) in conjunction with a signal analysis unit (18) to monitor a sequence of multiple heart pulses, hence to deduce the values of a sequence of multiple heart pulse intervals, and to analyse the sequence of multiple heart pulse intervals to deduce a risk parameter whose value enables those at risk of cardiac arrhythmia to be identified. The risk parameter may be calculated from a first measure, or alternatively by combining the first measure with a second measure, where the first measure is calculated from the ratio between the variability between successive intervals in the sequence, and the mean interval value, while the second measure relates to the proportion of cases in which a long interval is followed by another long interval in the sequence.
