The effects of i.v. prostaglandins (PGs) E2 and I2 on ouabain-induced cardiac arrhythmias were investigated in chloralose-anaesthetized cats. Bilateral vagotomy and guanethidine-pretreatment interventions were employed to elucidate the involvement of vagal and sympathetic neural influences in these effects. PGE2 (1 micrograms/kg/min i.v. infusion for 5 min) and PGI2 (4-16 microgram/kg i.v. bolus injections) effectively suppressed the ouabain-induced arrhythmias in a control group of cats. The bilateral vagotomy or guanethidine-pretreatment interventions did not significantly alter the antiarrhythmic effects of PGE2 and PGI2. It is concluded that the presence of functionally intact sympathetic and vagal nerve supply to the heart is not a prerequisite for the antiarrhythmic effects of i.v. administered PGE2 and PGI2. The possible role of direct action of these PGs on the myocardium is discussed.