The rate of progression of the degree of chronic aortic regurgitation (AR) is unknown. Furthermore, although left ventricular (LV) dilation has been studied in patients with severe AR, its rata and determining factors, and specifically, its relation to the degree of regurgitation remain to be established and have not previously been studied for mild and moderate AR. The purpose of this study was to explore the progression of chronic AR by 2- dimensional and Doppler echocardiography, and the relation of LV dilation to the fundamental regurgitant lesion and its progression in patients with a full spectrum of initial AR severity. We studied 127 patients with AR by 2- dimensional and Doppler echocardiography (69 men; 59 ± 21 years; 67 with mild, 45 with moderate, 15 with severe AR). AR increased in 38 patients (30%) (25% of mild, 44% of moderate, and 50% of moderate to severe lesions; p <0.006). The ratio of proximal AR jet height to LV outflow tract height also increased (30.3 ± 17.5% vs 35.2 ± 19.7%; p <0.0001). Initial LV volumes and mass were larger in patients with more severe AR and increased significantly during follow-up (138 ± 53 to 164 ± 70 ml; 59 ± 32 to 71.7 ± 42 ml; 203 ± 89 to 241 ± 114 g; p <0.0001). LV volumes and mass increased faster in patients with more severe AR, and in those in whom the degree of AR progressed more rapidly. Finally, patients with bicuspid aortic valve (n = 21) had a higher prevalence of severe AR than patients with tricuspid aortic valves (52% vs 4%; p <0.001). In conclusion, AR is a progressive disease not only in patients with severe AR but also in those with mild and moderate regurgitation. Patients with more severe AR have larger left ventricles that also dilate more rapidly.