Tc-99m-teboroxime is prepared by the addition of 370-3700 MBq (10-100 mCi) of Tc-99m pertechnetate (obtained from a Mo-99/Tc-99m generator) to a lyophilized Cardiotec(R) kit, and then heating the kit at 100 C for 15 min. After cooling, Tc-99m-teboroxime is ready for patient administration. The radiochemical purity (RCP) of Tc-99m-teboroxime is consistently greater than 90%; this can be confirmed by paper chromatography. Tc-99m-teboroxime is stable in the kit for at least 6 h following its preparation. Teboroxime (both the Tc-99m and Tc-99 forms) is prepared by template synthesis as shown in the simplified reaction.