“Mr. A,” a 41-year-old man, had regularly taken illicit methamphetamine, from 1 g to 5 g per week, by intranasal inhalation over the past 5 years. Because of irritability, suspiciousness, and agitation, he was brought to our emergency department. The patient’s family reported that neither he nor the family had a medical history of syncope, palpitation, chest pain, or cardiovascular disease, and he was not taking any prescription or over-the-counter medications. Physical examinations and laboratory tests, including serum electrolytes, were unremarkable, except for urine toxicology testing, which showed a methamphetamine level exceeding 2,000 ng/ml. A 12-lead electrocardiogram (ECG) demonstrated normal sinus rhythm (NSR), with a rate of 70 beat/min and a QTc of 487 msec, according to Fridericia’s formula. Nevertheless, an ECG obtained 3 months before, when the result of urine drug screening was negative, revealed NSR with a rate of 70 beat/min and a QTc of 371 msec. Four days after this admission, the patient’s QTc increased to 410 msec, and his urine methamphetamine level was 722 ng/ml. No significant findings were reported in his echocardiography and 24-hour Holter monitoring. Finally, he was discharged in stable condition with a normal QTc interval. Five months later, he was brought to our hospital because of similar symptoms. His ECG revealed NSR with a rate of 60 beat/min and a QTc of 476 msec according to Fridericia’s formula, and urine methamphetamine was 944 ng/ml. At the time of discharge, his QTc interval decreased to 405 msec, and urine methamphetamine level was 0.