Abstract: Starting from 99TcmO4- and at 0.1 MPa CO pressure conditions, the important starting material 99Tcm(CO)3(H2O3+ is synthesized. By ligand exchanging of this starting material with isonitrile ligand CHI (Cyclohexylisonitrile), the complex 99Tcm(CO)3(CHI)3+ is prepared. Its ra-diochemical purity is more than 90%, and it is stable over 6 h at room temperature. The biodistri-bution of this new complex in normal mice indicates that it has some myocardial uptake and maintained well in it, the values of heart uptake at 5 min and 60 min post-injection are (13. 59±2.12)% ID/g and (13. 87±1.54)%ID/g, respectively. Unfortunately the uptakes of non-targets, such as liver and lung, are also quite high. Compared with 99TcmN-CHI and 99Tcm-CHI, the tricarbonyl complex 99Tcm(CO)3(CHI)3+ has the most suitable properties for myocardial imaging.