A compound of the general formula (M.sup.1).sub.n --Q--(M.sup.2).sub.1-n --L--A I wherein: n is 0 or 1; M.sup.1 is an amino group; Q is an aromatic heterocyclic group containing a basic nitrogen atom; M.sup.2 is an imino group; L is a template group; and A is an acidic group, or an ester or amide derivative thereof, or a sulphonamide group; and pharmaceutically acceptable salts and pro-drugs thereof, for use in the treatment of a disease in which platelet aggregation mediated by the binding of adhesion molecules to GPIIb-IIIa is involved. Novel compounds are also disclosed.