The purpose of this study was to investigate the safety and efficacy of a novel vascular sealing device that incorporates a unique low-profile balloon-positioning catheter and a procoagulant delivered after diagnostic cardiac catheterization and percutaneous transluminal coronary angioplasty (PTCA) procedures. Current management of the vascular access site after percutaneous interventions is associated with patient discomfort and complications. Based on previously reported successful results in canine models, we proceeded with this first human feasibility and safety study. Immediately after an invasive procedure, the sealing device was successfully deployed at the femoral arterial access site in 24 of 24 procedures (diagnostic 19, PTCA 5). All patients were followed up at 1 month with clinical assessment, ankle-brachial index measurement, and Doppler ultrasound. Successful hemostasis was achieved in all patients. The activated clotting time before sealing device deployment was 125.5 +/- 22.2 and 267.8 +/- 60.0 seconds for diagnostic and PTCA patients, respectively. The time to hemostasis was 2.5 +/- 0.9 minutes for diagnostic and 6.0 +/- 2.2 minutes for PTCA patients. No major complications were observed. Coagulation markers (fibrinogen, D-dimer, thrombin-antithrombin-3 complex, and prothrombin fragment 1 and 2) measured before and after sealing device deployment did not reveal excessive intravascular thrombin generation or other coagulopathy. This novel vascular sealing device successfully achieves safe and effective vascular access site hemostasis immediately after cardiac catheterization and PTCA. These promising first human results will need to be confirmed by a multicenter randomized trial.