Contrast media cause a variety of effects on the cardiovascular system both hemodynamic and electrophysiologic in nature. These effects are mainly related to the physico-chemical characteristics of the compounds and are less pronounced with low osmolar nonionic than with ionic contrast media. Nonetheless there is still room for further improvement in the features of the nonionic agents. Iomeprol is a new nonionic contrast medium which, with its low osmolality and toxicity and very low viscosity, proved to be safe and well tolerated during clinical trials in cardioangiography.