18 The non-invasive assessment of left ventricular function with simple indices, such as left ventricular volumes and ejection fraction (LVEF), offers significant diagnostic and prognostic implications in the entire spectrum of cardiac diseases. Equilibrium radionuclide ventriculography (RNV) is a well validated technique for this purpose. Based on the principle that the amount of radioactivity emitted by technetium-99m (99mTc)-pertechnate labeled erythrocytes in the cardiac chambers is proportional to the amount of bloodcontained, reproducible and accurate LVEF measurements can be obtained, with practically no geometric assumptions regarding heart shape. However, the development of other imaging techniques, mostly echocardiography and secondarily cardiac magnetic resonance has led to a decline in the use of RNV. This is due to easiness, cost and availability issues and also because competitive modalities can offer reliable anatomic and functional information and hence they can address a variety of clinical scenarios in one session. Nevertheless, RNV still remains a reliable method in clinical conditions, in which the detection of small changes in LVEF may be important in clinical decision-making, such as in patients undergoing cardiotoxic chemotherapy, when the images of different methods are of suboptimal quality or unobtainable, or there is discordance between clinical judgment and imaging results. In this respect the more recently introduced gated single photon emission tomography (SPET) myocardial perfusion imaging has not demonstrated equivalent reliability, in terms of independence from a variety of factors and accuracy of measurements on a per-patient basis. The purpose of this review is to present the features of RNV, and to define its role in the evaluation of cardiac function in the current era of medical imaging.