Rapid development of effective surgical methods for correcting congenital and acquired cardiovascular lesions has created a need for precise roentgen demonstration of the cardiac chambers. Increasing experience with angiocardiographic technics has shown the diagnostic advantages of the selective injection of contrast medium through accurately positioned intracardiac catheters or needles. To overcome the resistance to flow in long catheters or needles with small cross-section diameters, mechanical or automatic high-pressure injecting devices must be employed. In addition, adequate opacification requires the use of a concentrated iodinated medium. Seventy per cent sodium acetrizoate (Urokon) has been widely employed in angiocardiography, but several reports calling attention to its nephrotoxic and neurotoxic effects have recently been published (1–4). A fatality following angiocardiography in which 70 per cent Urokon was used led us to abandon this medium in favor of 90 per cent sodium diatrizoate (Hypaque)...