The purpose of this study was to point out the existing methods and to describe and evaluate the accuracy of new, original, "Geometric-count-based" (GCB) method, based on radionuclide ventriculography, for the measurement of left ventricular volumes compaired to the contrast ventriculography. By having done this, the aim was to compare the accuracy of GCB method and other two radionuclide methods available for left ventricular volume measurements: Count-bases Massardo method and gated blood pool SPECT method. In GCB method count based data from radionuclide ventriculography were combined with geometric ones assuming a prolate ellipsoid left ventricular's shape with identical short axes. The following equation for computing left ventricular end-diastolic volume was developed: EDV = 2 x c x M x C(tot)/C(max), (1) where: 2c--manually drown short axis of prolate ellipsoid (left ventricle) at end-diastolic frame, M-calibrated pixel size, C(tot)--total counts in left ventricular's region of interest at end-diastolic frame, C(max)--maximum pixel counts in left ventricular's region of interest. Physical experiments with two different heart shaped phantoms were used to compare volumes assessed by all three radionuclide methods with the true volumes. The true volumes of cylindrical and ellipsoid phantoms of 112.5 ml and 190.5 ml, were computed to be 114 ml and 196 ml by our GCB method, 168 ml and 180 ml by Massardo method and 142 ml and 222 ml by gated blood pool SPECT methods, respectively. In clinical study, in 65 patients volumes assessed by radionuclide methods were compared to volumes measured using single plane contrast ventriculography as a gold standard. A good correlation of our original method was obtained with a contrast ventriculography for both EDV/m2 and ESV/m2 (r = 0.94, r = 0.92), slightly lower for Massardo method (EDV/m2: r = 0.90, ESV/m2 : r = 0.89) and significantly lower for gated blood pool SPECT (EDV/m2: r = 0.85, ESV/m2: r = 0.81, p < 0.01). In conclusion, both, phantom and clinical studies indicate that GCB radionuclide method is accurate, noninvasive for left ventricular volumes' measurement and should be widely used in everyday clinical practice.