Aortic distensibility is decreased in patients with coronary artery disease (CAD) and the angiographically normal aorta. To determine if the same is true in patients with aortic stenosis and post-stenotic dilatation, two groups were studied. Group A consisted of 15 patients with post-stenotic aortic dilatation and normal coronary arteries, and group B, 14 patients with post-stenotic aortic dilatation and CAD. The patients were compared to 18 normal subjects. The area of the first 6 cm of the aorta above the valve obtained by aortography was planimetered and the mean diameters were calculated. Distensibility was calculated using the formula: (formula; see text) Distensibility was greater in group A (2.5 +- .4 cm2.dynes-1) compared to group B (1.0 +- 8 cm2.dynes-1, p less than 0.001). Distensibility in normal subjects reported recently from this laboratory (3.4 +- .4 cm2.dynes-1) was greater compared to both groups A and B (p less than 0.001). Thus, distensibility was decreased in patients with post-stenotic aortic dilatation. The further decrease in distensibility in patients with co-existing coronary artery disease may be partially related to abnormal nutrition of the arterial wall since the vasa vasorum of the ascending aorta are derived from the coronary arteries.