Multiple intracardiac catheters are often necessary for electrophysiological study (EPS) and radiofrequency (RF) ablation therapy. Therefore, multiple venous sheath placement in one femoral vein is always required for multiple intracardiac catheter insertion. The vascular complications incurred by placement of multiple sheaths have not been fully studied. We utilized duplex ultrasonography to assess the femoral veins before and after the procedure. This study consisted of 52 patients (68 femoral veins) who underwent EPS and RF ablation therapy. Up to three sheaths were inserted into a single femoral vein. Nonocclusive deep vein thrombosis (DVT) occurred in 12/68 veins (17.6%) of 11 patients on the day following the procedure. Thrombosis regressed spontaneously in 11 veins and persisted in 1 vein at 1-week follow-up. The venous diameter significantly decreased the day after the procedure (8.7 +/- 1.2 mm vs 5.3 +/- 1.5 mm, P < 0.001), but recovered by the 1-week follow-up (7.9 +/- 1.7 mm, P = 0.07) in the 12 veins. Short-term placement of multiple venous sheaths in a single femoral vein appears to be safe. Nonetheless, nonocclusive DVT does occur in a significant number of patients. Although thrombosis regressed and the outcome appeared to be benign in most patients, close follow-up to avoid potential vascular complications is necessary.