Abstract: Objective To investigate the image characteristic of ⁹⁹Tc^m-4, 9-diaza-3, 3, 10, 10-tetramethyldodecan-2, 11-dione dioxime (⁹⁹Tc^m-HL91) in the ischemic myocardium, thus explore the possibility of ⁹⁹Tc^m-HL91 in assessment of ischemic but viable myocardium. Methods Eighteen patients with cardiac infarction went ⁹⁹Tc^m-sestamibi(⁹⁹Tc^m-MIBI)SPECT and ⁹⁹Tc^m-HL91 SPECT. Average radioactivity of ischemic area and normal area were respectively obtained by region of interest on heart short axis images.The radioactivity ratios of target (ischemic area)-to-non target (normal area) were calculated. Results In 10 patients the positive ⁹⁹Tc^m-HL91 uptake was shown in the defect region of ⁹⁹Tc^m-MIBI images. In the other cases, similar signs have not been found. Conclusions ⁹⁹Tc^m-HL91 may be selectively uptaken by ischemic and hypoxic but viable myocardium. The combination of ⁹⁹Tc^m-MIBI and ⁹⁹Tc^m-HL91 SPECT may be more helpful for accurate evaluation of hypoxic viable myocardium.