AbstractSystemic heparinization has been advocated as preventive for thrombotic and embolic complications of arterial catheterization. To test this hypothesis, 95 patients undergoing coronary angiography via the percutaneous femoral arterial approach were randomized into heparinized and nonheparinized groups.Evaluation for thrombotic and embolic complications by clinical means and noninvasive electrical impedance flow measurements in the lower limbs was performed precatheterization, postcatheterization, and at 4 and 24 hr. Clinical data reveal loss of distal leg pulses in 11% (5/47) of the nonheparinized group, with two of these individuals developing signs of claudication and requiring embolectomy. No individuals (0/48) in the heparinized group lost distal leg pulses. Immediate, 4‐hr, and 24‐hr postcatheterization bloodflow was 12%, 10%, and 12% lower, respectively, in the catheterized limb of those in the nonheparinized group. At 24 hr 52% of the nonheparinized group had bloodflow levels lower than the precatheterization levels in the right (catheterized) extremity, while 2% (2/48) of the heparinized group had a similar reduction.One possible complication of excess bleeding was noted with heparin.It is concluded that systemic heparinization is safe and can be an important adjunct in the reduction of thromboembolic complications of percutaneous coronary angiogra