It has been reported that young children taking β-blockers may be at risk of hypoglycaemia when fasting. However, hypoglycaemia is not listed as a side effect of β-blockers in the British National Formulary for Children. We present five patients (out of approximately 570 patients at our institution who were prescribed regular β-blockers over the same time period) who had severe hypoglycaemic episodes whilst taking β-blockers for prevention of arrhythmia. We demonstrate how such an episode may be misinterpreted as an arrhythmic event and how this could lead to inappropriate escalation of medical therapy or even implantation of an automatic implantable cardiac defibrillator.