The presence and functional role of the swelling-activated Cl(-) current (I(Cl(swell))) in rabbit cardiac Purkinje cells was examined using patch-clamp methodology. Extracellular hypotonicity (210 or 135 mOsm) activated an outwardly rectifying, time-independent current with a reversal potential close to the calculated Cl(-) equilibrium potential (E(Cl)). The magnitude of this current was related to tonicity of the superfusate. The current was blocked by 0.5 mM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS). These features are comparable to those of I(Cl(swell)) found in sinoatrial nodal, atrial, and ventricular myocytes. I(Cl(swell)) activation at 210 and 135 mOsm depolarized the resting membrane potential with 6 and 10 mV and shortened the action potential by approximately 18 and approximately 33%, respectively. DIDS partially reversed I(Cl(swell))-induced action potential changes. We conclude that I(Cl(swell)) is present in Purkinje cells and its activation leads to action potential shortening and resting membrane potential depolarization, both of which can promote the development of reentrant arrhythmias.