A method is desbribed for mapping the electrical impedance cardiac signal on the anterior thoracic surface in man. A sinusoidal current was injected through electrodes placed around the neck and lower abdomen and voltage differences were measured with a single exploratory electrode at 30 well defined position on the thorax and upper abdomen. The expected interbeat variability was minimised by digital processing. Different pattern of dZ/dt, the first derivative of the cardiac impedance change were obtained at different points on the thoracic showing the additional information and discrimination provided by impedance surface mapping. The results of this work suggest that classical impedance cardiography detects mainly blood flow changes in the large upper thoracic vessels of the clavicular region. With the present method it is possible to visualise the effect of changes in heart volume and shape on the local impedance distribution and the spreading of blood flow related impedance changes across the thoracic and upper abdominal surfaces.