Dual antiplatelet therapy is the cornerstone of treatment of coronary heart disease after coronary stent implantation. The interindividual response to this therapy is not uniform, however. There are subgroups of patients, where no anticipated antiplatelet effect to either aspirin, clopidogrel or both is reached. The term of aspirin/clopidogrel resistance has been introduced few years ago, most recently it was substituted by more suitable term - high on-treatment residual platelet reactivity (HPR). Although there are many assays to monitor antiplatelet therapy, uncertainty still remains about the correlation of HPR with ischemic vascular events (in-stent thrombosis, myocardial infarction, etc.). Thus platelet aggregation testing is considered to be the most promising method to indicate inappropriate/low response to aspirin/clopidogrel, however the best suited method is not established yet. Up-to date light transmittance aggregometry is widely accepted as golden standard, nonetheless labour intensive and difficult to standardize. On the other hand many point-of-care aggregation testing methods like PFA-100, VerifyNOW, Multiplate etc. have been introduced, their role in clinical practice is uncertain, however. The biggest challenge of today is to determine platelet function assay, which could reliably indicate future ischemic vascular events;moreover it could be potentially used to tailor antiplatelet therapy and precede these events. It was demonstrated, that gene polymorphism - CYP2C19*2 and CYP2C9*3 loss of function is conjugated with an increased occurrence of stent thrombosis. Within the project we also plan to examine 4 alleles which have not been examined in detail before.