Aortic augmentation index, the amount by which aortic pressure is “augmented” above the first systolic shoulder of the aortic pulse wave, expressed as a ratio of aortic pulse pressure, is thought to relate to arterial properties. In particular it has been cited as an index of “arterial wave reflection” related to arterial stiffness. However, it could also be influenced by the characteristics of ventricular ejection. The objective of the present study was to examine the relation of AIx to arterial stiffness and ventricular contraction-relaxation. We studied 74 asymptomatic subjects, aged 24–89 years, 7–15 subjects per decade) using an Aloka α10 ultrasound system with 3MHz cardiac probe to perform conventional echocardiography, obtain tissue Doppler ventricular velocities and mitral flow velocities. Using the same system with a 10MHz linear vascular transducer, ECG-referenced echo-tracking of the carotid and femoral arteries was used to obtain carotid augmentation index (AIx) and carotid-femoral pulse wave velocity (PWV). The relation of AIx to PWV and ventricular tissue velocities was examined using univariable and multivariable regression analysis. On multivariable analysis, entering age, mean arterial blood pressure and all measures correlated with AIx on univariable analysis (including PWV), AIx was independently negatively correlated only with heart rate and the ratio of diastolic to atrial mitral valve flow velocities (E/A). Together these variables explained 39% of the variability in AIx. These results suggest that AIx is more closely related to ventricular contraction-relaxation than to arterial properties.