Videodensitometry allows to obtain both left and right ventricular ejection fraction (EF) and aortic or pulmonary regurgitant fraction (RGF) from the wash-out curve of contrast medium. We developed this technique to digital densitometry and integrated it in the standard digital image acquisition system 'Digitron' using Siemens user's library. Sources of error like scatter radiation, veiling glare, accumulation of iodine in tissue, and inhomogeneous contrast mixing were considered by using ECG gated image subtraction, background reference regions, data fit to ideal wash-out curves and calculation of EF and RGF exclusively from density differences. The method was validated by phantom studies in which simulated angiocardiograms were generated with given values of EF (50 to 70%) and RGF (0 to 45%). The results tended to overestimate RGF by up to 10 percent points, when image contrast was high and the ventricle was masked poorly by the lead shutters. In the clinical setting, the reliability of the results can be judged from the fit of the wash-out curve presented automatically on the screen on a semi-logarithmic scale. The technique is available to the physician in the catheterization laboratory on-line during or immediately after the examination, which facilitates routine use.