In a case of acute thrombosis on mitral Starr valve two-dimensional doppler-echocardiography rapidly showed that parts of the transprosthetic jets had disappeared, while conventional continuous wave doppler ultrasound confirmed the presence of a severe haemodynamic obstacle. With colour-coded doppler ultrasound, there only remained a jet that was parallel to the posterior wall of the left ventricle. This jet was of unusual pattern, with the presence of turbulence and high velocities in aliasing colour. The effectiveness of a thrombolytic treatment was demonstrated by the reappearance of the missing diastolic jets with return to normal velocities. Comparison between a post-thrombolysis colour-coded doppler examination and a reference examination confirmed that the valve was now functioning normally. Thus, while conventional doppler recordings accurately quantify prosthetic dysfunctions leading to stenosis, two-dimensional doppler recordings rapidly provide an anatomical information. By showing changes in the transprosthetic jets they indicate the precise location and extent of valve obstruction.