An apparatus and a method for detecting cardiac atrial fibrillation events in an EKG signal. The method comprises the steps of detecting a portion of an EKG signal comprising cardiac beats; measuring the duration of a gap in the detected portion of the EKG signal; and computing two or more inter-beat intervals. The computed interval is outputted if the gap in the portion of the EKG signal is not more than a fraction alpha of the computed interval. The method further includes the steps of computing the variance of the inter-beat intervals and classifying the portions of the EKG signal as indicative of an atrial fibrillation event. During classification, the inter-beat interval variance of the portion of the EKG signal that exceeds a pre-determined value V is indicative of an atrial fibrillation event. The method further includes discarding portions of the EKG signal classified as indicative of atrial fibrillation if said portions have a duration less than a pre-determined threshold S and annotating the EKG signal. The non-discarded portions of the EKG signals having inter-beat variances that exceed V are annotated as atrial fibrillation events.