Normalization of Doppler indices of diastolic dysfunction during pacing is a sign of ischemic mitral regurgitation. Twenty-three patients with angina who were undergoing diagnostic cardiac catheterization underwent cardiac pacing with simultaneous hemodynamic and Doppler echocardiographic evaluation to assess the effects of pacing-induced ischemic on mitral valve velocity. Seventeen patients had significant coronary artery disease, and six patients had normal coronary arteries. Doppler and hemodynamic measurements were performed at rest and immediately after pacing was discontinued to 91% +/- 7% of maximal predicted heart rate. Seven patients experienced new or significant increases in severity of mitral regurgitation after pacing as revealed by Doppler examination. This group had a significant increase (p = 0.007) in early but not in late peak filling velocities immediately after pacing was discontinued, with a resultant decrease in late to early ratios, which decreased from 1.01% +/- 0.12 to 0.70% +/- 0.19 (p = 0.006). Left ventricular end-diastolic pressure increased significantly from 16.7% +/- 6.8 mm Hg to 29.4% +/- 5.3 mm Hg after cardiac pacing (p less than 0.001). Patients with coronary disease who did not develop mitral regurgitation also had significant increases in left ventricular end-diastolic pressure from 18.7% +/- 5.8 mm Hg to 24.3% +/- 8.6 mm Hg (p less than 0.05). There were no changes in late or early wave amplitude, late to early ratio, or other Doppler measurements in any of the other groups. We conclude that mitral regurgitation caused by pacing-induced myocardial ischemia normalizes Doppler indices of mitral inflow, which in turn, may mask persistent or worsened left ventricular diastolic dysfunction. 