A comparison was performed between technetium-99m tetrofosmin myocardial perfusion tomography at baseline and after nitrate administration, using a 2-day protocol, and rest-reinjection thallium-201 single-photon emission tomography (SPET) studies in order to assess whether nitrates enhance the detection of viable myocardium with 99mTc-tetrofosmin. Fifteen patients with coronary artery disease, previous myocardial infarction and a left ventricular ejection fraction <40% underwent 201Tl rest-injection and 99mTc-tetrofosmin baseline-postnitroglycerin (0.4 mg sublingually) SPET studies, within 48 h. Tomograms based on the three spatial planes were divided into 15 segments and regional tracer uptake was quantitatively analysed. Viability was defined as presence of tracer uptake >/=50% of peak activity on baseline studies or after reversibility. The percentage of peak activity of 99mTc-tetrofosmin at baseline correlated with that of 201Tl (r=0.82, P <0.001). On baseline 99mTc-tetrofosmin studies, 73 of the 225 segments that were analysed had <50% of peak activity. Fifteen percent of these segments showed reversibility after nitrate administration, with an increase in 99mTc-tetrofosmin uptake from 40%+/-9% to 57%+/-9% of peak activity (P=0.003). All reversible segments after nitrate administration had viability criteria on 201Tl studies, but 20 segments that were non-viable on 99mTc-tetrofosmin studies were viable on 201Tl studies. Using a threshold value of >/=40% of peak activity, only seven segments remained non-viable on 99mTc-tetrofosmin studies. Overall agreement between 99mTc-tetrofosmin with nitrates and 201Tl-reinjection regarding the presence of myocardial viability was 90%. Detection of myocardial viability with 99mTc-tetrofosmin was enhanced after nitrate administration, correlating with viability criteria observed on thallium studies.