To evaluate whether nitroglycerin administered before the injection of sestamibi improves the detection of viable but hypoperfused myocardium, 41 post-infarction patients with left ventricular dysfunction underwent echocardiography and SPET at rest and after nitrate administration. In 25 revascularized patients, perfusion at rest and contractility were assessed 3-4 months after coronary artery bypass grafting. Perfusion (PI) and wall motion indices (WMI) were calculated for each revascularized area. There was a strong correlation between contractility and perfusion defect (r = 0.58, P < 0.0001). Nitrates significantly reduced the number of perfusion defects in hypokinetic (delta PI = 0.25 +/- 0.66) and akinetic (delta PI = 0.32 +/- 0.62), but not in dyskinetic (delta PI = 0.08 +/- 0.62), segments. Twenty-five revascularized patients had 110 asynergic segments and 136 segments with a resting perfusion defect. Function improved in 42% and perfusion in 64% of segments after surgery. Viable segments had a lower PI at rest (2.78 +/- 1.38 vs 3.86 +/- 1.29, P < 0.001) and a lower WMI (2.46 +/- 0.50 vs 2.79 +/- 0.59, P = 0.002). Nitrates reduced the number of perfusion defects slightly more in viable than non-viable segments (delta PI = 0.58 +/- 0.89 vs 0.30 +/- 0.46, P = 0.06). Contractility and perfusion at rest were the most important predictors of functional recovery. The sensitivity and specificity in predicting contractile improvement were 74% and 64% for resting SPET respectively, and 80% and 50% for nitrate SPET respectively. Nitrate administration significantly reduces perfusion defects in asynergic regions; however, its usefulness in predicting contractile recovery may be limited owing to its low specificity. Contractility and sestamibi uptake at rest were the strongest predictors of post-operative wall motion improvement.