The preparation of the compounds is quite different to that of all other potential radiopharmaceuticals being from pertechnetate heated in an aromatic solvent in the presence of aluminium catalysts. The desired technetium compounds must be taken up by the myocardium in proportion to blood flow. There is one major requirement that must be met in order that an injected tracer accurately depicts myocardial perfusion. As more sophisticated procedures are developed to treat myocardial ischaemia it becomes more critical to know tissue perfusion, as opposed to vessel blood flow. A large number of derivatives were made and tested in animals and showed promising myocardial uptake. The correspondence between the rabbit and human data is good but a few compounds, MEG, EEG, EAI, that possess a single substituent alpha to the isonitrile group stand out as being different. All compounds were taken up and retained by the myocardium when examined in rats, rabbits, dogs, cats and pigs.