Quinine, the levo-isomer of quinidine, is used to treat malaria and is also commonly employed in the United States to treat leg cramps. The ECG shown here is from a 74 year old woman who was receiving 200 mg of quinine twice daily to treat her leg cramps. She had no known heart disease, was not receiving any other medications and her serum electrolytes were normal. The ST, T and U changes seen on this tracing are similar to those caused by quinidine.