The effect of contrast media on the left ventricular function of the heart was assessed by left coronary administration of contrast media using canine models. Following insertion of the catheter into the left coronary artery, 0.5 ml/kg of a test solution was injected at a rate of 1 ml/s. The test solutions included isotonic saline, meglumine/sodium diatrizoate, iopamidol and ioxaglate. The mean systemic pressure, left ventricular end-systolic and end-diastolic pressures and the first derivative of left ventricular pressure were continuously measured until five min post-injection. Left ventricular function decreased immediately by 15 s post-injection and recovered quickly by one min. The inhibition of myocardial contractility was observed with diatrizoate and ioxaglate to the same degree. These changes were statistically more pronounced than those with iopamidol, which showed changes similar to those with saline in all parameters except for the positive inotropic effects. These observations suggest that not only hyperosmolality but also ionic composition and chemotoxicity are the factors responsible for the myocardial depression and that no single factor dominates in their effects.