(3S)-Hydroxyquinidine is the major active metabolite of quinidine, an antiarrhythmic alkaloid. It retains pharmacological activity similar to its parent compound and is primarily used in laboratory research, including pharmacokinetic/pharmacodynamic studies, as a reference standard for LC-MS/MS analysis of quinidine metabolism, and in investigations of cardiac electrophysiology and antimalarial effects. This specialty chemical is employed in pharmaceutical R&D and analytical applications, not for direct clinical therapeutic use.