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A man in his 20s presented to the emergency department with acute limb weakness. Laboratory investigations revealed severe hypokalaemia with serum potassium of 2.0 mmol/L. The 12-lead ECG at admission demonstrated distinctive ST-segment changes in the right precordial leads ( figure 1). Echocardiography showed no structural heart disease. Intravenous potassium supplementation was administered, promptly correcting the electrolyte disturbance to 4.2 mmol/L. A repeat ECG showed complete normalisation of the previously observed ST-segment abnormalities (figure 2). After full recovery, the patient underwent pharmacological provocation testing with intravenous flecainide (2 mg/kg over 10 min) in a monitored electrophysiology setting. The drug challenge reproducibly elicited an ECG pattern identical to that observed during the initial hypokalaemic episode (figure 3).