The purpose of this investigation was to compare the Ejection Fraction values simultaneously obtained with the Nuclear Stethoscope and with Cineangiography, in 25 patients (17M-8W) subjected to diagnostic cardiac catheterization. In all patients the determination of Ejection Fraction with the Nuclear Stethoscope always preceded the Cineangiography. Ejection Fraction values obtained with Nuclear Stethoscope change from 32 to 75%; those calculated with Cineangiography, between 18 and 88%. The average Ejection Fraction values obtained with Nuclear Stethoscope (59 +/- 13%) doesn't differ significantly from Cineangiography (59 +/- 21%). There was a direct relationship between Ejection Fraction determined by the Nuclear Stethoscope and Cineangiography (r = 0.93; p less than 0.001). In the obtained results the Authors point out that the Ejection Fraction with Nuclear Stethoscope gives assurance in most patients, although in some particular conditions Nuclear Stethoscope provides Ejection Fraction values which differ from those obtained with Cineangiography. They conclude that Nuclear Stethoscope, for its safe, repeating and simple application, is a methodology of useful employment for Ejection Fraction determination in the single patient, which allows a correct definition of the prognosis and a conforming therapeutic strategy.