In a randomized, double-blind, controlled study, we compared heparinized and nonheparinized infusions for the maintenance of perioperative arterial catheter patency and the incidence of subsequent radial arterial occlusion. Two-hundred patients were randomized into 2 groups to receive heparinized (group H, n = 100) or nonheparinized (group S, n = 100) flush solutions. Radial and ulnar blood flows were assessed using Doppler probe and pulse oximetry before, just after, and 24 h after decannulation by the same investigator. The cannulation site was examined for complications such as hematoma, nerve injury, and infection. The mean duration of cannulations was 378 +/- 159.0 min in group H and 332 +/- 154.6 min in group S. The mean number of corrective interventions caused by dampening of the pressure wave (mean number of positional changes [group S, 1.5 +/- 2.0; group H, 1.4 +/- 3.8] and mean number of manual flushes [group S, 1.3 +/- 1.7; group H, 1.2 +/- 1.2]) was not significantly different in both groups. After decannulation, partial or total occlusion developed in 20 group H patients and 16 group S patients (not significant). The incidence of occlusion was correlated to the presence of hematoma at the puncture site after decannulation (P = 0.013), long duration of cannulation (P = 0.04), and age < 65 yr (P = 0.009). In conclusion, there is no significant difference between heparinized and nonheparinized flush solutions for the maintenance of perioperative radial artery catheter patency.