In has been suggested that cardiac catheters traversing competent heart valves may induce valvular regurgitation. To evaluate this possibility, continuous-wave and pulsed Doppler echocardiographic studies were performed immediately before, during and immediately after removal of various catheters in a total of 47 adult patients without clinical evidence of valvular regurgitation. With the tip of a 7Fr balloon flotation catheter positioned in the pulmonary artery, 9 of 36 patients (25%) had pulmonary regurgitation documented by continuous-wave Doppler. Evidence for regurgitation by pulsed Doppler examination was noted in 4 of these 9, with the regurgitant signal extending a mean of 1.8 cm into the right ventricular outflow tract. Similarly, a tricuspid regurgitant signal was present in 10 to 37 patients (27%) by continuous-wave Doppler and in 6 of these 10 by pulsed Doppler, with a mean regurgitant signal depth of 2.3 cm. Doppler examination also was performed in 7 patients (2 with aortic regurgitation) with a 7Fr pigtail catheter across the aortic valve, and in 4 patients (1 with tricuspid regurgitation) with a 6Fr bipolar pacing catheter across the tricuspid valve. Catheter removal resulted in no change in either the presence or absence of a regurgitant signal, or in the regurgitant signal depth in any of the patients studied. It is concluded that standard cardiac catheters neither induce Doppler-detected valvular regurgitation, nor do they affect the retrograde distance to which an existing regurgitant signal can be mapped.