The percutaneous arm approach through the radial or brachial artery for diagnostic cardiac catheterization has advantages, such as a lower incidence of access-site complications and decreased patient discomfort, particularly when smaller diameter catheters are employed. However, the pressure produced by high-flow jets of contrast material exiting from an end-hole against the vascular wall can cause coronary dissection or myocardial blushing. To avoid this type of complication, we designed and developed a new miniature (4 French) catheter with two side-holes for coronary angiography. Under conditions similar to those of a clinical situation, we obtained the relationship between the pressure produced by the jets exiting from an end-hole and the force with which the tip of the catheter was pushed against the vascular wall. The presence of the side-holes substantially decreased the pressure at forces ranging between 0 and 15 gf, and at all injection rates (2.0 3.5 ml/second), but their location did not affect the pressure. In a preliminary clinical study, the new catheters with side-holes were feasible and effective for coronary angiography through the radial artery. Furthermore, the distribution of contrast material decreased the incidence of dislodgement of the catheter from the coronary ostia and enabled good visualization of the coronary ostia and proximal branches.