Peri-procedural medications. An intravenous bolus of 5,000 U of unfractionated heparin will be given immediately following the insertion of the venous sheath. An additional approximately 2,000 to 3,000 U of heparin will be added if the procedural time exceeds 1 h. Following the procedure, oral warfarin will be prescribed and adjusted according to the international normalized ratio to be between 2 and 2.5 for all patients. If there would be contraindications for warfarin, aspirin (100 mg/day) and clopidogrel (75 mg/day) will be prescribed indefinitely. Immediately after the PADN procedure, all medications (diuretics, sildenafil, bosentan, beraprost, digoxin etc.) will be discontinued for 24h.