Thanks for your relevant query; heart functions affect problems due to methadone overdose. Fatal attack may come because of an overdose of methadone also it will impact the abnormal heart beat it leads to unregularly function of heart muscles. The failure of this functions guide to pulmonary edema is a disease causing the lungs. The lungs become full with fluid and causing the chest pain also results palpitation and breathing trouble. My recommendation is to visit your doctor as soon as possible do not approach to this symptoms simply.