2-Mercaptocyclopentanecarboxylic acid compounds (I) and their optical isomers and acid addition salts are new. 2-Mercaptocyclopentanecarboxylic acid compounds of formula (I) and their optical isomers and acid addition salts are new. R 1 : H or COR 4; R 4 : 1-6C alkyl or aryl or cyclopentane carboxylic acid group of formula (II); R 2 : NR 5R 6; R 5, R 6 : H, 1-6C alkyl, group, a nitrogen-containing heterocyclic group, aryl or heteroaryl; R 3 : H or 1-6C alkyl; m : 1-6; and n : 0-2. An independent claim is included for a composition comprising (I) in combination with one or more inert, non-toxic, excipients or carriers. [Image] [Image] ACTIVITY : Cardiant; Antianginal; Antiinflammatory; Vasotropic; Thrombolytic; Cerebroprotective; Vulnerary; Nootropic. MECHANISM OF ACTION : Thrombin-activatable fibrinolysis inhibitor (TAFI). (I) were tested for their TAF inhibitory activity using purified human TAFI. The results showed that the IC 5 0value of (I) was 6.7+- 0.6 nM.