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The determination of cardiac output and central blood volume is of considerable importance, not only in cardiac research but in the diagnosis and treatment of heart disease. At present, the most clinically adaptable method of determining these parameters is the indicator-dilution technique. However, analysis of indicator-dilution curves is laborious, requiring twenty to forty minutes of a skilled operator's time. A simple instrument has been devised which permits the determination of cardiac output and central blood volume in less than one minute. The computer described in this paper makes use of an electronically-generated curve which is displayed on a CRT, and optically superimposed on the actual indicator-dilution curve. Three manual controls, used to match the curves, yield the desired parameters. The computer may be used to analyze curves within the following ranges: Curve amplitude (2A) = 2.5 to 10 cm; Period (T) = 2.5 to 10 sec; Time constant (CT) = (0.25 to 1) Ã T sec; Injection (I) = 5 to 12.5 mg; Calibration (M) = 5 to 1.2 cm/mg/liter; Cardiac output = 0 to 48 liters/min; Mean transit time = 25 sec full scale.