The risk of significant complications from contrast media is greatest in angiocardiography. Contrast media effects on central cardiovascular function include electrophysiologic effects such as bradycardia, hypotension, and ventricular arrhythmias; hemodynamic effects such as hypotension and blood flow changes; and metabolic effects such as transient hypocalcemia. Differences between ionic and nonionic media are less obvious in clinical studies but become apparent in carefully controlled animal experiments. Evidence indicates that nonionic media have less propensity to cause ventricular arrhythmias and bradycardia than ionic media. In addition, nonionic agents do not adversely affect left ventricular regional function and produced no negative inotropic effects in the presence of coronary stenosis. Unlike ionic diatrizoate, nonionic iohexol did not significantly interact with the calcium blocker, verapamil. Iohexol also produced no increase in lung water or in femoral blood flow, while diatrizoate produced increases in both. It is concluded that iohexol has fewer and less severe negative effects on central cardiovascular function than standard ionic media.