Methadone poisoning has become more common in the pediatric population due to extensive use of methadone maintenance therapy (MMT). It is associated with decreased level of consciousness, coma, respiratory distress and cardiac intoxication. The cardiac complications have been reported to be QT prolongation, torsade de pointes, coronary artery disease, arrhythmia, stress cardiomyopathy and death. We herein report two pediatric patients with accidental methadone poisoning who developed stress cardiomyopathy and cardiac failure. The first case was a 4-yaer-old girl and the second one was an 18-month-old girl both being accidentally poisoned with methadone syrup and were brought with decreased level of consciousness. Both were diagnosed to suffer from congestive heart failure based on echocardiography. However, the first case passed away despite appropriate treatment, while the second one survived the condition and was discharged with good condition and was symptom free at 6-month follow-up.