Several studies have demonstrated the value of Doppler ultrasound as a means of measuring gradients across cardiac valves. However, in view of sudden variations in cardiac output gradients should be measured simultaneously by Doppler and catheterization in order to validate the former method and determine its accuracy. We conducted a prospective study with simultaneous recordings in 78 patients with aortic valve stenosis (33) or mitral valve stenosis (19) or cardiac valve prosthesis (26). Mean age of the patients was 55 +/- 14 years, and 50% of them were male. Subjects with pure or predominant regurgitation were excluded from the study. In the whole of the population studied, correlation between Doppler ultrasound and haemodynamics was very good with r = 0.98, p less than 0.001 for maximum gradient and r = 0.96, p less than 0.001 for mean gradient. The perfect simultaneity of the haemodynamic and ultrasonic recordings was confirmed by comparing the duration of gradients measured by the two methods (r = 0.996, p less than 0.001). There also was very close correlation between ultrasounds and catheter in patients with mitral stenosis (maximum gradient r = 0.98, p less than 0.001; mean gradient r = 0.97, p less than 0.001). Mean Doppler-catheter differences were not significant, and no underestimation by Doppler reached or exceeded 5 mmHg. Correlations were also satisfactory in patients with aortic stenosis (maximum gradient r = 0.97, p less than 0.01; mean gradient r = 0.90, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)