A quantitative description of the Na^+ channel properties is essential in electropharmacological studies on the modes of action of local anesthtics and antiarrhythmics. The recent advance in techniques of isolating single cardiomyocytes and voltage-clamping the total membrane area of the whole-cell with single patch electrodes have provided a useful tool for Na^+ current studies in heart tissues. We successfully recorded Na^+ channel currents under the physiological conditions (140 mM [Na^+]_0) nad analyzed the gating linetics of current flow according to hodgkin-Hucley model, so that the time course of Na^+ current could be described with four voltage-dependent variables (m_∞, τ_m, h_∞ and τ_h) and two constants (<g_Na>^^^- and E_Na). In Na^+ current studies use of embryonic chick heart clees was found to be advantageous because of better ”space-clamp” due to their spheroidal shapes and the small cell size.