The development of techniques that allow the high fidelity measurement of small scale ionic currents ushered in a new era of investigation into the role of ion channels in the physiologic and pathophysiologic function of excitable tissue. Based upon the formation of a high resistance (gigaohm) seal with the membrane of the cell being studied, these "patch clamp" techniques have improved our understanding of a wide variety of cardiac disease states with respect to diagnosis, treatment and prognosis. This review outlines the basic principles underlying the patch clamp technique, including the properties of biological membranes and ion channels, and provides an elementary summary of its application to the recording of cardiac ionic currents, with a particular focus on issues related to myocyte isolation, electrode manufacturing and the voltage clamp configuration.