The model works with a user-defined average heart rate in beats per minute (BPM). It simulates cardiac arrhythmia of normal breathing by varying the heart rate sinusoidally following the respiration frequency that can also be selected by the user in cycles per minute (CPM). The maximal variation is defined as percentage of the selected mean heart rate and can be set between 0 and 30%. Because the duration of diastole varies with heart rate the filling time varies and so will the stroke volume. This results in variation of the Sys2 but not the Sys1 component since the amplitude of the Sys1 depends on the strength of arterial acceleration and on the end diastolic blood pressure of the former heart beat whereas the amplitude of the Sys2 component depends on the stroke volume of the current heart beat. Respiratory variation of the difference between Sys1 and Sys2 during, for instance, deep breathing has often been demonstrated in real-life registrations.
Alternatively, the model simulates atrial fibrillation by generating random variation of the heart rate around the selected mean. The generated variation is distributed evenly around the mean.