Nicotine (10(-8) - 5 X 10(-5) M) had no effect on the rate of beating of the lizard or tortoise isolated right atria, but caused concentration-dependent positive chronotropic responses in spontaneously-beating isolated right atria of the guinea-pig. Furthermore, nicotine (10(-8) - 5 X 10(-5) M) had no effect on contractile tension of isolated, electrically-driven left atria of the tortoise; it induced a biphasic inotropic response in driven left atria of the rainbow lizard and produced a concentration-related positive inotropic response in electrically-driven isolated left atria of the guinea-pig.(ABSTRACT TRUNCATED AT 250 WORDS)