Despite catecholamines being lifesaving drugs, they can also be harmful. Adrenergic overload is one of the major causes of supra- and ventricular arrhythmias, which induce haemodynamic instability of critically ill patients. In this paper we will focus on the pathophysiology of atrial fibrillation (AF), the importance of adrenergic overload for triggering AF, the importance of the autonomic nervous system and we will challenge the importance of decreasing adrenergic load with selective and non-selective β-blockers, which have different effects on the metabolism of the severely ill. We will also emphasize the importance of an individual approach due to pharmacogenetic differences in β-adrenergic signalling.