Sticholysins I and II (St I/II) are cytolysins purified from the sea anemone Stichodactyla helianthus. In this study, we show their pharmacological action on guinea-pig and snail models in native and pH-denatured conditions in order to correlate the pharmacological findings with the pore-forming activity of both isoforms. In guinea-pig erythrocytes (𝑁 = 3), St II possessed higher haemolytic activity in comparison with St I and this activity was lost at an alkaline pH. In molluscan central neurons (𝑁 = 30), they irreversibly decreased the amplitude of the cholinergic response; St I (EC50 0.6 𝜇molL–1) was more potent than St II (EC50 > 6.6 𝜇molL–1) and they both increased the duration of the action potential; these effects were absent at an alkaline pH. In guinea-pig isolated atrium (𝑁 = 25), both increased the amplitude of the contraction force, but St II was more potent than St I (EC50 0.03 𝜇molL–1 and 0.3 𝜇molL–1, respectively) and this effect persisted at an alkaline pH. In summary, both cytolysins have neuroactive and cardioactive properties. The main mechanism in molluscan neurons seems to be associated with the cytolytic activity of these molecules, whereas in guinea-pig atrium, the existence of an additional pharmacological mechanism might be contributing to the observed effect.