Cardiac arrhythmias exhibit also a circadian variability. It is impressingly apparent in sustained ventricular tachycardia and sudden cardiac death. Adrenergic stimulation during morning hours, a physiologic event for the transition from nocturnal to diurnal activity, appears to be an important arrhythmogenic factor (25). The results of the BHAT-study show that beta blocking agents may substantially reduce the risk for sudden cardiac death during morning hours. This notion should thus be considered in treating patients at risk.