The delivery pressure at the catheter tip during angiography was studied by means of a miniature pressure transducer at the tip and side openings of cardiac catheters over a wide range of machine pressures (100 to 800 pounds per square inch [psi]). It is composed of a peak pressure and a plateau pressure. The peak pressure has a short duration (usually less than 0.2 seconds) but often exceeds 500 mm Hg even under a low machine pressure of 100 psi. The plateau pressure has a longer duration, lasting for two seconds or more when 60 ml of contrast substance are used. Under a high machine pressure of 500 psi or more, the plateau pressure reaches a level of 500 mm Hg. Both peak and plateau pressures fall exponentially with increased distance from catheter openings, and the flow of the surrounding fluids has no appreciable effect in the dissipation of the high velocity jet.