OBJECTIVE To study the effects of taurine (Tau) and tetrodotoxin (Tet) on cesium chloride (CsCl)-induced triggered activity and arrhythmia in anesthetized rabbits. METHODS With a cuffed endotracheal tube, the rabbit ventilation was maintained by a respirator. A Franzy's contact electrode catheter was advanced into the right ventricle through the right external jugular vein and positioned against the anteroapical endocardial surface to record the monophasic action potential (MAP). A catheter was placed into femoral vein for systemic drug administration. RESULTS CsCl (1 mmol L-1 iv) produced a decrease in the amplitude of MAP from 42.2 +/- 2.1 to 37.0 +/- 3.8 mV (P < 0.01), a prolongation of MAPD50 (156 +/- 22 to 209 +/- 26 ms, P < 0.01) or MAPD90 (205 +/- 25 to 250 +/- 20 ms, P < 0.01) and an early afterdepolarization (EAD) developed within 30 s after CsCl injection. The ventricular premature (VP) resulted from EAD triggered by CsCl. In the Tau (100 mg kg-1)- or Tet (10 micrograms kg-1)-pretreated group, not only was the amplitude of EAD decreased (Tau, 4.2 +/- 2.7; or Tet, 5.2 +/- 2.6, respectively vs 16.1 +/- 8.3 mv, P < 0.01), but also the duration of EAD was shortened (Tau, 695 +/- 164; or Tet, 492 +/- 172, respectively, vs 1068 +/- 166 ms, P < 0.01). The severity of triggered arrhythmia (TA) was alleviated and the incidence of TA was lowered within 30 min after iv CsCl by either Tau or Tet. CONCLUSIONS The depressant effects of Tau and Tet on EAD and VP induced by CsCl were involved in an increase of outward current or a decrease of an inward current.