A heart monitor for use as a non-invasive screening tool for identifying potential atrial fibrillation in patients comprises a sensor for producing an output waveform of the patients actual sinus rhythm, a processing unit arranged to store the normalized waveform of an ideal sinus rhythm and to compare the actual and ideal sinus rhythm waveforms and to produce an output dependant on the difference on a display. The value of the output is indicative of whether the patient is atrial fibrillation or other cardiac arrhythmia.
