The focal extracellular potential (FEP) described in this study is an electrophysiological signal related to the transmembrane potential (V_m) of cardiac myocytes that avoids the mechanical fragility, interference with contraction, and intracellular contact associated with conventional whole cell recording. One end of a frog ventricular myocyte was secured into a glass holding pipette. The FEP was measured differentially between this pipette and a bath pipette while the cell was voltage- or current-clamped by a third whole cell pipette. The FEP appeared as an amplitude-truncated action potential, while FEP duration accurately reflected the action potential duration (APD) at 90% repolarization (APD₉₀). FEP magnitude increased as the holding pipette K⁺ concentration ([K⁺]) was increased. The FEP-voltage relation was quasi-linear at negative V_m with a slope that increased with elevated holding pipette [K⁺]. Increasing the membrane conductance inside the holding pipette by adding amphotericin B or cromakalim linearized the FEP-voltage relation across all V_m. The FEP accurately reported electrical activation and APD₉₀ during changes of stimulation frequency and episodes of cellular stretch.