Background: Estimation of aortic pressure waveform provides clinical information regarding BP cardiovascular risk additional to the brachial blood pressure (BP). The effect of body position on central haemodynamics (BP, pulse pressure (PP) amplification (amp), augmentation index (AIx), augmentation pressure (AP), subendocardial viability ratio (SVR) have never been investigated. Aim/design: to investigate in a randomized cross over study changes in both the peripheral and central haemodynamics in supine and sitting position. Methods: Sixty one subjects referred for BP assessment were examined (36 males, mean age 50±12 yrs). Brachial and aortic waveforms were assessed in sitting and supine position. In each position: triplicate brachial BP measurements were performed; then 2 consecutive aortic pressure waveforms were estimated by applanation tonometry of the radial artery - pulse wave analysis and the use of transfer functions (Sphygmocor). The average of the last 2 brachial BP recordings was used in statistical analysis and for peripheral waveforms calibration. Results: Mean arterial BP did not differ significantly between the sitting and supine position (table). Brachial and aortic SBP, PP, AP, AIx were significantly higher in the supine position whereas DBP and PP amplification (ratio: brachial/aortic PP) significantly smaller. Moreover, significant alterations were observed in heart rate, ejection duration and SVR. Conclusions: Mean BP remained unchanged but the pulsatile BP component was higher in the supine position. This was more pronounced in the aorta, as shown by PP amplification, in part due to alterations in heart rate, wave reflections leading to alterations in coronary perfusion.