Amidine derivatives of the formula ##STR1## wherein R.sub.1 and R.sub.2, which may be the same or different, represent each a hydrogen atom or a lower alkyl group, or R.sub.1 and R.sub.2 together with an intermediary carbon atom and/or hetero atom may form a ring; X represents ##STR2## (wherein R.sub.8 represents a hydrogen atom, a lower alkyl group, or --CH.sub.2 COOR.sub.9, where R.sub.9 represents a hydrogen atom or a lower alkyl group; Z represents a single bond, --CH.sub.2 --, --CH.sub.2 CH.sub.2 --, or --CH.dbd.CH--); R.sub.3 represents a hydrogen or chlorine atom, methoxy group, nitro group, or amino group; Y represents --CH.sub.2 CH.sub.2 --, --CH.dbd.CH--, --CH.sub.2 O--, or --OCH.sub.2 --; R.sub.4 represents a hydrogen atom, methoxy group, benzoyl group, nitro group, or amino group; and R.sub.5, R.sub.6 and R.sub.7, which may be the same or different, represent each a hydrogen atom, lower alkyl group, cycloalkyl group, aralkyl group, substituted alkyl group, substituted aralkyl group, or amino group, or R.sub.5 and R.sub.7 may form a ring, or salts thereof have an excellent cardiotonic activity and can be used as cardiotonics.