RATIONALE AND OBJECTIVES Bolus injection of iodinated contrast media has been observed to alter myocardial mechanical function, but the consequences on cellular metabolism are poorly documented. Modifications of metabolic parameters (intracellular pH as well as adenosine triphosphate [ATP], phosphocreatine, and inorganic phosphate contents) and of mechanical function (coronary flow, heart rate, and left ventricular developed pressure) were simultaneously recorded on isolated rat hearts perfused over 2 minutes with a high osmolality contrast medium (HOCM) and two low osmolality contrast media (LOCM). In addition, the effects of test solutions mimicking the ionicity and the osmolality of LOCM were evaluated. METHODS Isovolumic rat hearts were submitted to a 2-minute perfusion with oxygenated Radioselectan, Hexabrix, and Omnipaque (320 mgI/mL) at 37 degrees C. Metabolic parameters were obtained by P-31 nuclear magnetic resonance spectroscopy at 4.7 Tesla. Noniodinated ionic and nonionic solutions also were tested for comparison. RESULTS HOCM irreversibly impairs the metabolic and mechanical functions, whereas ionic and nonionic LOCM and test solutions induce transient cardiac failure but no permanent alteration of the metabolic or mechanical parameters. CONCLUSION In this protocol, HOCM causes irreversible degradation of the biochemical status and definitive heart failure, whereas ionic and nonionic LOCM only induce transient changes of myocardial function. Treatments with the LOCM do not induce any modification of the ATP and PCr content, and, at the end of the reperfusion period, the mechanical function is equivalent to that of control hearts. Depending on the ionic content of the solutions (iodinated or not), the evolution of the ventricular developed pressure after injection differs from one group of hearts to another. From these experiments, it is concluded that ionic imbalance and viscosity of the solutions, rather than iodine content or hyperosmolality, should be considered the causes of heart failure.