The effects of adding NaCl to the non-ionic contrast medium iohexol (Omnipaque) were investigated in the isolated rat heart. Iohexol (150 mgI/ml) with 0, 10, 20, 30, 50, 145 mM NaCl added and the ionic dimeric compound ioxaglate (Hexabrix 160 mgI/ml) containing approximately 75 mM NaCl were examined. Coronary flow rate (CFR), heart rate (HR), left ventricular developed pressure (LVDP) and myocardial high energy phosphate compounds at the end of the experiments were measured. In all groups examined the physiological changes following contrast media injection were only transient and the recovery to normal values of HR and LVDP occurred within 30 seconds. The contractile changes after contrast media exposure were dependent on the concentration of sodium added. The addition of 20 mM sodium to iohexol induced the least changes in LVDP. It is concluded from the present study that addition of sodium in the range of 20-40 mM to non-ionic contrast media, may reduce the immediate cardiac disturbances during coronary angiography.