The cause and duration of the thrombogenesis provoked by radiofrequency catheter ablation (RF-CA) was investigated by measuring the thrombin-antithrombin III complex (TAT) in 43 patients who underwent RF-CA and in 20 control subjects who underwent an electrophysiologic study. Blood samples were collected at 7 different times: before introducing the sheaths, during the ablation procedure and at 30 min, 6 and 24h, and 3 and 6 days after the procedure. Hepatocyte growth factor (HGF) was simultaneously measured in the ablation group. Plasma TAT concentration exhibited a double peaked pattern in the ablation group: the first peak occurred during the ablation procedure (42.8+/-15.5 ng/ml), and the second peak 3 days later. Plasma TAT at 3 days after the procedure was significantly higher than that of the control group (21.3+/-19.0 vs 2.5+/-1.4, p=0.0003). The first peak significantly correlated with the procedure time prior to the administration of heparin (r=0.669), but the second peak did not (r=0.132). A subgroup with a serum HGF >0.40 ng/ml at 6 h after the procedure exhibited a significantly high second peak. The thrombogenesis caused by RF-CA has 2 phases; in the acute phase, there is hemostasis during placement of the catheters, and in the delayed phase thrombogenesis is the result of endothelial damage from the RF current.