BACKGROUND AND PURPOSEThis study was designed to examine the antiarrhythmic efficacy and the underlying mechanisms of the benzyl-furoquinoline vasodilator, CIJ-3-2F, in rat cardiac preparations. EXPERIMENTAL APPROACHConduction electrograms and left ventricular pressure were determined in Langendorff-perfused hearts. Action potentials were assessed with microelectrode techniques, calcium transients by fura-2 fluorescence and ionic currents by whole-cell patch-clamp techniques. KEY RESULTSIn isolated hearts, CIJ-3-2F prolonged sinus cycle length, QT interval, Wenckebach cycle length, atrio-His bundle and His bundle-ventricular conduction intervals, refractory periods in atrium, AV node, His-Purkinje system and ventricle, and also increased left ventricular pressure. CIJ-3-2F reduced the incidences of both ischaemic and reperfusion-induced ventricular arrhythmias and prevented the induction of atrial tachyarrhythmias. In both atrial and papillary muscles, CIJ-3-2F decreased upstroke velocity and prolonged duration of the action potential. In ventricular myocytes, CIJ-3-2F moderately increased the amplitude of [Ca 2+ ]i transients and cell shortening. CIJ-3-2F inhibited the transient outward K + current (Ito) (IC50 = 4.4 μM) with accelerated inactivation, a slower rate of recovery from inactivation and use-dependency. CIJ-3-2F also suppressed the steady-state outward K + current (Iss, IC50 = 3.6 μM, maximum inhibition = 65.7%) and both the inward Na + current (INa, IC50 = 2.8 μM) and L-type Ca 2+ current (ICa,L, IC50 = 4.9 μM, maximum inhibition = 69.4%). CONCLUSIONS AND IMPLICATIONSCIJ-3-2F blocked Na + and Ito channels and, to some extent, also blocked Ca 2+ and Iss channels, modifying cardiac electromechanical function. These effects are likely to underlie its antiarrhythmic properties. AbbreviationsAERP, atrial effective refractory period; APA, action potential amplitude; APD25, 50, 90, action potential duration measured at 25, 50 and 90% repolarization; CIJ-3