The invention provides a method and system for analyzing an ECG signal to diagnose a heart condition of an individual. A sequence HBi of consecutive heart beat durations in an ECG signal is obtained. One or more first parameters are calculated in a calculation involving pairs of HBi and HBi-m, where m is a first predetermined integer and HBi-m is the duration of the heart beat that occurred m heart beats before the ith heart beat. One or more second parameters are calculated in a calculation involving pairs of HBi and HBBi-n, where n is second predetermined integer different from m. A diagnostic parameter is then calculated using the plurality of first parameters and the plurality of second parameters. The diagnostic parameter is compared to a predetermined threshold, and a diagnosis is made based on the comparison.