An Ag-AgCl electrode for recording monophasic action potentials by pressure contact is described. The electrode is mounted in a hand-held support designed for epicardial recordings during open-heart surgery from both the anterior and lateral walls of the left ventricle with minimal displacement of the heart. The support allows the electrode to be manipulated without the need for direct vision by the surgeon to any desired position while ensuring perpendicular apposition of the electrode without risk of damage to the myocardium. The permanently mounted electrode is also suitable for animal experiments. The electrode may be used for endocardial recordings in animals by direct puncture. Either a straight or curved electrode may be chosen as dictated by the recording site. The monophasic action potentials recorded by this electrode are of a high quality in terms of configuration, lack of drift, and amplitude.