Research in intermediary metabolism depends on the use of radioisotopes. In cardiology, isotopes have become essential both for research and clinical use. In experimental cardiology, isotopes are used for the determination of coronary blood flow and for the identification of receptors, among others. The measurement of coronary flow and the viability of the heart muscle in man by positron emission tomography (PET) scan also relies on the use of isotopes. Where and when did the use of isotopes in medicine and cardiology commence?...