Isolated vagus‐heart preparations from guinea‐pigs have been used for a comparative study of the ability of curare‐like drugs to block the effects of preganglionic stimulation of the vagi on the heart,in vitro. The following drugs all had this property and have been arranged in order of decreasing potency in this respect: hexafluorenium, gallamine, laudexium, decamethonium, tubocurarine, suxamethonium and succinyldisulphoch