When there are runs of wide complex beats, the distinction between supraventricular beats conducted aberrantly and beats arising in the ventricles may be more difficult. In patients with atrial fibrillation as the underlying rhythm, as in the example shown here, the RR interval preceding the run of wide complex beats, the coupling interval of the first beat of the run, the RR intervals of the beats within the run and then the RR interval between the last beat of the run and the next beat should be considered. Before going to the next page, try to decide whether the 4 consecutive wide complex beats in this example are aberrantly conducted or ventricular in origin.