A theory of streamline flow of a viscous liquid was applied to the calculation of cardiac and pulmonary parameters (minute volume, stroke volume, right heart, pulmonary and left heart blood volumes) in a radiocardiographic model based on the modified gamma function. The practical feasibility of the formulations was tested using a physical flow model. The cardiopulmonary blood volumes measured from 14 normal subjects were consistent with the results obtained by more complex techniques. The present method is manageable on a small computer and is well suited to clinical routine use in connection with standard single detector 113In(m) radiocardiography.