The aim of this study was to develop a widely applicable model for circulatory indicator dispersion which could describe the pharmacokinetics of early drug distribution. The model assumes that the substance is injected into the right atrium and measured in the aorta. The dilution curve results from the dispersion and recirculation of the indicator in the body. The concentration time curve in the aorta, r, can be described as r = c0 + g* r, where g is the transport function of the body and c0 is the concentration time course, which is measured for the first time in the aorta. If the body transport function is known, then the aortic dilution curve of a drug can be predicted for different elimination rates and injection times. The site of interest can be chosen arbitrarily, i.e. the concentration of inflow into the kidney or any other organ can be described.