The objective of this clinical study is to evaluate the safety and performance of the IASD System II in the treatment of heart failure patients with elevated left atrial pressure, who remain symptomatic despite appropriate medical management.

Key Inclusion Criteria:

1. Chronic symptomatic Heart Failure (HF) documented by one or more of the following:

   1. New York Heart Association (NYHA) Class II/III/ambulatory class IV symptoms (Paroxysmal nocturnal dyspnea, Orthopnea, Dyspnea on mild or moderate exertion) at screening visit; or signs (Any rales post cough, Chest x-ray demonstrating pulmonary congestion,) within past 12 months;
   2. One hospital admission for which HF was a major component of the hospitalization within the 12 months prior to study entry (transient heart failure in the context of myocardial infarction does not qualify);
   3. On-going management with recommended heart failure medications and comorbidities for several months according to the guidelines (2012 ESC Guidelines for diagnosis and Treatment of Acute and Chronic Heart Failure).

2. Age ≥ 40 years old

3. Left ventricular ejection fraction (obtained by echocardiography) ≥ 40%

4. Elevated left ventricular filling pressures with a gradient compared to CVP documented by :

   1. PCWP or LVEDP at rest ≥ 15 mmHg, and greater than CVP, OR
   2. PCWP during supine bike exercise ≥ 25mm Hg, and CVP < 20 mm Hg

Key Exclusion Criteria:

3. Severe heart failure defined as:

1. ACC/AHA/ESC Stage D heart failure, Non-ambulatory NYHA Class IV HF;
2. Fick Cardiac Index < 2.0 L/min/m2
3. Requiring inotropic infusion (continuous or intermittent) within the past 6 months
4. Patient is on the cardiac transplant waiting list 4. Inability to perform 6 Minute Walk Test 5. Known significant coronary artery disease (stenosis >70%) 6. History of stroke, transient ischemic attack (TIA), deep vein thrombosis (DVT), or pulmonary emboli within the past 6 months 7. Known severe carotid artery stenosis (> 70%) 8. Presence of significant valve disease defined by echocardiography as: a) Mitral valve regurgitation defined as grade >2+ MR b) Tricuspid valve regurgitation defined as grade ≥ 2+ TR; c) Aortic valve disease defined as ≥ 2+ AR or moderate AS