BACKGROUND Aortic function is an important determinant of pressure and flow in the entire cardiovascular system. This study aimed at evaluating segmental differences of aortic function and composition, in order to understand their clinical implications. METHODS The thoracic aorta from each of 20 healthy pigs was divided into four and the abdominal into three segments. From the stress-strain curves, relationships between elastic modulus and stress were obtained for low (part I), physiologic (part II) and high (part III) stresses. Linear regression analysis was performed. RESULTS No differences were found in the intercepts and slopes for part I. Significant differences were found in the intercepts and slopes between the thoracic and abdominal segments for part II, and in the slopes for part III, suggesting that the distal segments became progressively stiffer. Histologic examination disclosed higher concentrations of elastin in the proximal and collagen in the distal aortic wall. Aortic wall thickness reduced from proximal to distal aorta. Multiple regression analysis showed good correlations between elastic moduli and either elastin in part I (r=0.640) or collagen in part III (r=0.803). CONCLUSIONS The elastic properties and composition vary in different aortic segments. These differences should be taken into consideration when aortic function is determined in clinical practice.