Echocardiography will be performed at 3 month and 6 months following the procedure. Echocardiographic studies will be done using a Vivid 7 ultrasound system with a standard imaging transducer (General Electric Co., Easton Turnpike, Connecticut). All of the measurements will be performed according the recommendations of the American Society of Echocardiography (12). Digital echocardiographic data that contained a minimum of 3 consecutive beats (or 5 beats in cases of atrial fibrillation) will be acquired and analyzed. Right ventricular (RV) systolic pressure is equal to systolic PAP in the absence of pulmonary stenosis. Systolic PAP is equal to the sum of the right atrial (RA) pressure and the RV-to-RA pressure gradient during systole. RA pressure will be estimated based on the echocardiographic features of the inferior vena cava and assigned a standard value (13). The RV-to-RA pressure gradient will be calculated as 4vt2 using the modified Bernoulli equation, where vt is the velocity of the tricuspid regurgitation jet in m/s. The mean PAP will be estimated according to the velocity of the pulmonary regurgitation jet in m/s. The tricuspid excursion index (Tei) (14) is defined as (A-B)/B, where A is the time interval between the end and the onset of tricuspid annular diastolic velocity, and B is the duration of tricuspid annular systolic velocity (or the RV ejection time). PA compliance for patients will be calculated as the stroke volume divided by pulse pressure (systolic PAP minus diastolic PAP). Hemodynamic measurements and blood oxygen pressure/saturation determinations from the RA, RV, and PA will be performed as previously described using right heart catheterization before and immediately after the PADN procedure. These measurements will be repeated at 24 h, 3 months and 12 months. Measurements of resting RA pressure, RV pressure, systolic/diastolic/mean PAP, PA occlusive pressure (PAOP), cardiac output (CO) and mixed venous oxygen saturation will be recorded. The pulmonary vascular resistance (PVR) [PVR ¼(mean PAP- PAOP)/CO] and transpulmonary pressure gradient (TPG ¼ mean PAP- PAOP) will then be calculated. All of the measurements will be recorded at the end of expiration. Five criteria (15-17) will be used to evaluate whether a PAOP measurement was valid: 1) the PAOP was less than the diastolic PAP; 2) the tracing was comparable to the atrial pressure waveform; 3) the fluoroscopic image exhibited a stationary catheter following inflation; 4) free flow was present within the catheter (flush test); and 5) highly oxygenated blood (capillary) was obtained from the distal portion in the occlusion position. If the PAOP measurement was unreliable, the left ventricular end-diastolic pressure will then be measured and used rather than the PAOP.