Objective: Technetium 99m-N-MPO ([Tc-99m-N(mpo)(PNP5)](+)) is a cationic Tc-99m nitrido complex.The objective of this study is to evaluate its potential as a new radiotracer for myocardial perfusion imaging.METHODS: Biodistribution studies were performed in KM mice to compare the myocardial uptake of Tc-99m-N-MPO from noncardiac organs, such as the liver and lungs, with Tc-99m-sestamibi.Kinetics of blood clearance in rabbits was used.Planar imaging was performed and myocardial perfusion imaging was performed in rabbits and in swine respectively to evaluate the utility of Tc-99m-N-MPO as a myocardial perfusion imaging agent.RESULTS: Radiochemical purity of Tc-99m-N-MPO was over 90 % and stable for 6 hours at room temperature.Biodistribution studies demonstrated that this radiopharmaceutical localized selectively in the myocardium of mice, the cardiac uptake was 7.88±1.76,6.20 ±1.01, 5.17 ±1.65,3.30 ±1.38 and 2.38 ±1.00 %ID/g at 5,15, 30, 60 and 120min postinjection, respectively.Images showed liver uptake was decreased faster than cardiac uptake in rabbits , and the mean Tc-99m-N-MPO heart-to-liver activity ratio was 1.16, 1.44, 1.61 ,1.62, 1.65 and 1.51 at 5min,15min ,30min , 45min, 60min and 90min postinjection, respectively.The heart was distinguishable on scans at 15min.In contrast, the mean Tc-99m-MIBI heart-to-liver activity ratio was 0.81, 1.94, 1.15, 1.38, 1.43 and 1.86.The myocardial perfusion imaging in swine showed the defect regions with the Tc-99m-N-MPO.The tolerance of this drug in KM mice was 120 times as much as in humans.CONCLUSION: Tc-99m-N-MPO exhibits favorable stability, biological property and safety.The combination of favorable organ biodistribution and myocardial uptake with rapid liver clearance makes Tc-99m-N-MPO a very promising myocardial perfusion radiotracer worthy of further evaluation in various preclinical animal models.