To evaluate myocardial viability of patients (pts) with old myocardial infarction (OMI), we measured the rate of increase of diastolic coronary flow velocity (% increase) induced by intracoronary injection of iopamidol using a Doppler cathter. The tip of the catheter was placed at the proximal region of the left anterior descending artery (LAD) at a minimum of 2 cm proximal from the stenotic lesion. The sampling point was set 3 mm distal from the tip. The subjects consisted of 10 pts with revasculized anteroseptal OMI (G-O); 5 pts of angina pectoris (G-A); and 14 normal subjects (G-N). % increase of G-O (26.8±13.6) was significantly lower than that of G-A (52.9±15.0) and G-N (89.1±37.6). When we classified G-O in 4 pts with 90% stenosis (s) and 6 pts with less than 50% stenosis (O) according to the residual stenosis, the % increase of (S) (22.5±15.1) was lower than that of G-A (52.9±15.0), and (O) (29.8±13.0) was also lower than that of G-N (89.1±37.6). When we classified G-O according to the degree of the wall motion by left ventriculography, the % increase of the 7 pts with akinesis (21.2±11.5) was lower than that of the 3 pts with hypokinesis (40.0±7.6) and that of G-N (89.1±37.6). These results suggest that the % increase induced by intracoronary injection of iopamidol is a good index of the degree of myocardial viability.