Abrupt closure of a coronary artery after successful angioplasty remains a problem for the interventionalist. Many laboratories continue to administer heparin intravenously for 12 to 24 hours in an attempt to alleviate this problem. But prolonged heparin therapy delays sheath removal and may lead to groin and vascular complications, and so prolong the hospital stay. To test the hypothesis that subcutaneous heparin was as efficacious as intravenous heparin in preventing acute closure while reducing the vascular complications associated with extended sheath placement, we prospectively randomized 151 patients to two groups. The intravenous group, 77 patients, received continuous intravenous heparin at 1000 units/hour for 12 to 18 hours; the subcutaneous group, 74 patients, received 12,500 units subcutaneously every 12 hours for three doses after sheath removal 2 to 3 hours after the angioplasty. The activated clotting time immediately after the angioplasty was 401 +/- 108 seconds in subcutaneous group, as compared with 368 +/- 67 seconds in the intravenous group (p = 0.028). Patients receiving subcutaneous heparin continued to show adequate anticoagulation, with a PTT of 85 +/- 21 seconds obtained approximately 12 hours after the procedure. The PTT at discharge was statistically greater in the subcutaneous group, at 49.2 +/- 21 seconds, versus 35.6 +/- 13 seconds in the intravenous group (p < 0.001). Abrupt occlusion was similar in both groups, but the hematomas and bleeding/oozing in the intravenous group was significantly higher when compared with that of the subcutaneous group, 16 versus 6 (p = 0.026) and 26 versus 7 (p < or = 0.002), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)