Digital subtraction video densitometry is utilized in the determination of left ventricular ejection fraction. The mask mode subtracted video images obtained after a peripheral intravenous injection of a bolus of Renografin 76 are used in the derivation of a density-time curve. The left ventricular ejection fraction (LVEF) is computed by an algorithm described in this paper. Results for 15 patients are compared to the LVEF’s obtained by applying the area-length method to the same patient data. The left ventricular ejection fractions computed by both methods had a good correlation (r=0.96) in fifteen patients. © 1981 SPIE.