Resting Tc-99m-tetrofosmin (TF) uptake was compared with thallium (Tl-201) rest-redistribution (R-RD) uptake in patients with previous myocardial infarction (MI) and significant coronary artery disease (CAD) to assess the ability of TF to detect viable myocardium. We studied 30 patients (21 males and nine females, mean age 53.9 +/- 12.5 years) with prior MI and left ventricular dysfunction who had been referred for coronary revascularization procedures. Myocardial single photon emission computed tomography (SPECT) images were obtained 1 h after injection of 750 MBq of TF. Within I week of the TT study, R-RD Tl-201 SPECT imaging was performed after injection of 111 MBq of Tl-201. Quantitative analysis was performed in 21 segments. Viability was defined as the presence of tracer uptake greater than 50% of the peak activity on baseline studies or after reversibility. There was significant correlation between the quantitative regional R-RD Tl-201 activity and the resting TF activity (r=0.88, P<0.001). Quantitative analysis showed that the uptake of the two tracers was comparable in normal segments as well as in segments with fixed Tl-201 defects. In contrast, in segments with reversible Tl-201 defects, TF uptake was significantly greater than resting Tl-201 uptake, but lower than R-RD Tl-201 uptake. There were 52 segments (47% of the severely reduced segments on TF images) that showed no viability with TF, but were viable on the redistribution Tl-201 studies. We conclude that quantitative resting TF SPECT underestimates the presence of viable myocardium compared with R-RD Tl-201 imaging on the basis of using 50% of the peak activity as the viability threshold. ((C) 2001 Lippincott Williams & Wilkins).