Objective: Current arterial transfer functions have low capability in predicti ng aortic augmentation index(AIx) from radial pulse contour(RPC), because of the difficulty in accurately identifying the merging point(inflection point) in the derived aortic pulse contour(APC). We hypothesize that the formation time betwe en each characteristic wave in APC is about one-third of ejection duration(ED/3 ). We sought to assess the accuracy of ED/3 in identifying the merging point in APC as compared to the conventional differential method. In addition, we sought to derive the AIx from RPC based on an arterial transfer function and the ED/3 m ethod. Methods: APC and RPC sequences were measured digitally and simultaneously in 60 subjects(37 males; aged 60±10 years). An ensemble-averaged RPCto-APC t ransfer function was determined from 30 randomly selected subjects and was used to derive APC sequences in the 30 additional subjects. The accuracy of AIx predi cted from RPC was determined. Results: In patients with a clearly identifiable m erging point in APC, the ED/3 method identified the merging point of measured AP C within 1.97±0.60 ms of that identified by the conventional differential metho d, with identical AIx. The AIx and merging point of derived APC using the ED/3 m ethod were also within 0.22±1.01%and 1.81±1.64 ms, respectively, of those of the measured APC using the conventional differential method. The accuracy of the predicted AIx was independent of age, sex, body-mass index and presence of hyp ertension. Conclusion: In a quiet resting state, the ED/3 is an alternative meth od for identifying the merging point in APC. In conjunction with transfer-funct ion technique, AIx can be derived accurately from RPC. Objective: Current arterial transfer functions have low capability in predicti ng aortic augmentation index (AIx) from radial pulse contour (RPC), because of the difficulty in accurately identifying the merging point (inflection point) in the derived aortic pulse contour (APC). We sought to assess the accuracy of ED / 3 in identifying the merging point in APC as compared to the conventional differential (ED / 3). We hypothesize that the formation time betwe en each characteristic wave in APC is about one- method. In addition, we sought to derive the AIx from RPC based on an arterial transfer function and the ED / 3 m ethod. APC and RPC sequences were measured digitally and simultaneously in 60 subjects (37 males; aged 60 ± 10 years ). An ensemble-averaged RPCto-APC t ransfer function was determined from 30 randomly selected subjects and was used to derive APC sequences in the 30 additional subjects. The accuracy of AIx predi cted from RPC was determined. Results: In patients with a clear identifiable m erging point in APC, the ED / 3 method identified the merging point of measured AP C within 1.97 ± 0.60 ms of that identified by the conventional differential metho d, with identical AIx. The AIx and merging point of derived APC using the ED / 3 m ethod were also within 0.22 ± 1.01% and 1.81 ± 1.64 ms, respectively, of those of the APC using the conventional differential method. The accuracy of the predicted AIx was independent of age, sex, body -mass index and presence of hyp ertension. Conclusion: In a quiet resting state, the ED / 3 is an alternative meth od for identifying the merging point in APC. In conjunction with transfer-funct ion technique, AIx can be derived accurately from RPC .