The authors studied the effect of the non-ionic radiopaque substance Omnipaque-350 on the central hemodynamics and myocardial contractility. A comprehensive angiographic examination was conducted in 25 patients. Omnipaque-350, when administered intravascularly, was found to induce the same general reactions as ionic triiod-containing radiopaque. It did not exert direct myocardiodepressive effect; yet, upon intracoronary administration it caused uniform changes in myocardial contractility and elasticity which corresponded to transitory alterations in its perfusion. During left ventriculography, Omnipaque-350 as compared with Urografin-76, has less marked hypervolemic properties and a less significant impact on the central hemodynamics and the pump function of the heart.