Introduction: Artemether and lumefantrine was registered as Riamet in Switzerland in 1999 and is commonly used in Keningau Hospital for managing uncomplicated malaria. Riamet works at the food vacoule of the malarial parasite, where they interfere with the conversion of heme into haemozoin. Case description: We report a case of Riamet induced prolonged corrected QT interval (QTc) in a 37 year old gentleman admitted for severe malaria (hypotension) with normal QTc of 420msc on presentation. Upon starting Riamet, he developed bradycardia and ECG showed sinus bradycardia with prolonged QTc of 551msec and no arrythmias. Echocardiography showed no structural heart abnormalities. All electrolytes were within normal range. He was monitored in cardiac care unit with decision to complete 6 doses of Riamet. Patient was started on Dopamine infusion which maintained his blood pressure and heart rate within normal range. 5 days post Riamet completion, his heart rate improved and dopamine infusion was tapered off and QTc normalized to 407msc. Discussion: The most common mechanism of drugs causing QT inter-val prolongation is by blocking the human ether-à-go-go related gene (hERG) potassium channel. Blockage of the hEGR channel lengthens ventricular re-polarization and duration of ventricular action potential which is reflected in ECG as prolonged QT interval. In the in-vitro whole cell patch clamp study, lumefantrine and its metabolite desbu-tyl-lumefantrine showed a concentration-dependent inhibition of the hERG current. The period of QTc prolongation was 3.5 to 4 days after the last dose of the standard 6 dose regimen. Conclusion: Riamet induced prolonged QTc is a very rare complication. A baseline electrocardiography is therefore imminent for every patient prior to initiation of this medication to avoid cardiac arrythmias.