The development of fatty acids labelled with iodine-123 is reviewed. The variety of methods for producing 123I and introducing radioiodine into the molecule is discussed and the important points of the biochemical background are recalled with the aim of finding a broad application for 123I-labelled fatty acids. The results of the pharmacokinetic studies and biochemical analyses are presented as they prove that both 17-123I-heptadecanoic acid (IHA) and 15-(p-123I-phenyl)pentadecanoic acid (IPPA) exhibit analogous behaviour to that of the naturally occurring fatty acids. Clinical applications demonstrated two fields of importance: applications solely for imaging the heart and assessment of myocardial turnover rates of fatty acids for functional diagnosis. Moreover, very recent studies show that the provision of information about prognosis of myocardial diseases and the applied cardiological therapy appear to be possible.