Objective To investigate the effects of anxiety and anti - anxiety therapy on vascular endothelium function and platelet activation in patients with acute coronary syndrome (ACS).Methods One hundred and thirty -nine ACS patients were enrolled in this prospective and controlled clinical study from January 2009 through December 2010.Patients with severe heart failure,liver and renal dysfunction,infection,allergy to benzodiazepines and taking antipsychotic drugs in recent 2 weeks as well as patients unable to complete the questionnaire were excluded.All these patients were divided into the anxiety group ( n =68 ) and the non - anxiety group ( n =71 ) according to Hamilton Anxiety Scale (HAMA).The plasma levels of NO,ET,CD62p,CD63 and flow- mediated diastolic functions (FMD) of humeral arteries were measured.The patients in anxiety group were randomly assigned to group A ( n =34 ) and group B ( n =34).Lorazepam in a dose of 0.5 mg twice a day and Vitamin B6 in dose of 10 mg twice a day as placebo were prescribed for patients of Group A and B respectively.After 2 weeks,all above variables of group A and group B were measured once again as well as the score of Hamilton Anxiety Scale.The chi - square test was used for constituent ratios,while t - test was applied to analysis of differences in above variables between two groups.Results The plasma level of NO and FMD of humeral artery in the anxiety group were significantly lower than those in the non -anxiety group (t =2.090 and 2.558,P =0.038 and 0.012,respectively),and the plasma levels of ET,CD62p and CD63 in the anxiety group were significantly higher than those in the non - anxiety group ( t =2.082,2.042 and 2.145,P =0.039,0.043 and 0.034,respectively).There were no statistical differences in all above variables as well as HAMA score between group A and group B before anti - anxiety treatment.Two weeks after treatment,the level of NO and FMD of humeral artery in group A were significantly higher than those in group B ( t =2.821 and 2.246,P =0,006 and 0.028,respectively) and the levels of ET,CD62p,CD63 and HAMA score in group A were significantly lower than those in group B ( t =2.107,3.242,2.079 and 7.779,P =0.039,0.002,0.041 and ＜0.01,respectively).Conclusions Anxiety mood markedly aggravates the disorder of vascular endothelial function and platelet activation,and both of them can be improved by anti - anxiety therapy.Consequently,the intervention in anxiety mood may improve the outcomes of ACS patients.