Continuous wave Doppler echocardiography is an accurate and reproducible method for determination of intracardiac pressure gradients in stenotic valve lesions and right-sided regurgitant lesions. Twenty-three patients with either mitral or aortic regurgitation underwent simultaneous continuous wave Doppler and dual catheter pressure recordings to determine if instantaneous pressure gradients can be accurately determined by Doppler ultrasound in left-sided regurgitant valve lesions. Using the modified Bernoulli equation, the maximal and mean pressure gradients between the left ventricle and left atrium were determined by continuous wave Doppler ultrasound in patients with mitral regurgitation and compared with simultaneous catheter-derived pressures. The mean and end-diastolic pressure gradients between the aorta and left ventricle were determined by continuous wave Doppler ultrasound in patients with aortic regurgitation and compared with simultaneous catheter-derived pressures. Diastolic half-times by both continuous wave Doppler ultrasound and catheter pressures were compared in patients with aortic regurgitation. There was a linear correlation between the mean gradients in all patients (r = 0.94; SEE = 6 mm Hg) with a similar correlation between the instantaneous gradients (r = 0.98; SEE = 8 mm Hg). There was a linear correlation between diastolic half-times by catheter and Doppler ultrasound (r = 0.95; SEE = 39 ms). As with other valvular lesions, continuous wave Doppler echocardiography can be used in patients with mitral or aortic regurgitation to accurately determine intracardiac pressure gradients.