Factors related to progression of nonrheumatic aortic stenosis (AS) were analyzed in 29 adult patients who underwent serial hemodynamic studies over a mean of 71 months. AS was congenital in 8 patients and degenerative in 21. The patients were divided into 2 groups on the basis of the change in aortic valve area between the 2 studies. Twelve patients had a greater than or equal to 25% reduction in aortic valve area (Group I) and 17 patients had less than 25% decrease in aortic valve area (Group II). There were no significant differences between the 2 groups in age, interval between studies, cardiac output, left ventricular end-diastolic pressure, left ventricular peak systolic pressure and origin of AS (congenital or degenerative). Group I patients had significantly larger initial aortic valve areas than did Group II patients (1.3 +/- 0.9 cm2 versus 0.8 +/- 0.4 cm2, p = 0.02). Also, the initial peak transaortic pressure gradients were lower in Group I than in Group II (27 +/- 19 versus 58 +/- 38 mm Hg, p = 0.01). Group I patients had a significantly greater increase in pressure gradient and a greater reduction in cardiac output than did Group II patients (24 +/- 21 mm Hg in Group I versus -0.1 +/- 24.5 mm Hg in Group II, p = 0.01, and -1.0 +/- 1.3 liters/min in Group I versus 0.10 +/- 1.4 liters/min in Group II, p = 0.03). Thus, AS progressed in 41% of a selected group of patients who underwent repeated cardiac catheterization.(ABSTRACT TRUNCATED AT 250 WORDS)