The purpose of the trial is to evaluate the wireless monitoring of pulmonary artery pressure using the CardioMEMS HF Pressure Measurement System in adult subjects with NYHA Class III Heart Failure.

The trial is designed to demonstrate that the CardioMEMS Sensor can be positioned in the right or left pulmonary artery, and that Sensor pressure measurements correlate to standardized methods of intra-cardiac pressure measurements post-sensor implant and at the 60 day visit. Safety will be monitored by the occurrence of adverse events throughout the trial.

Inclusion Criteria:

1. Subject is male or female, at least 18 years of age
2. Subjects of childbearing age who have a negative serum pregnancy test, and at screening have agreed to use a reliable mechanical or hormonal form of conception during the study.
3. Subject has a diagnosis of New York Heart Association (NYHA) Class III HF at screening and at baseline.
4. Subject is able and willing to provide written informed consent or the subject guardian is able and willing to provide informed consent.
5. Subject has life expectancy of 1-2 years.

Exclusion Criteria:

1. Subject has unstable medical condition or impairment other than a medical condition associated with HF which would significantly increase the subject's morbidity or mortality risk.
2. Subject is unable to tolerate a right heart catheterization.
3. Subject is planned to undergo a heart transplantation or cardiac surgery within 2 months after enrollment.
4. Subject has permanent indwelling central venous catheter.
5. Subject has history of myocardial infarction (MI), unstable angina, stroke, transient ischemic attack, or intractable arrhythmias within last 2 months.
6. Subject has history of congenital heart disease or prosthetic valve on right side.
7. Subject has unstable hypertension.
8. Subject has a known coagulability disease state.
9. Subject has a known hypersensitivity and/or allergy to aspirin and clopidogrel.
10. Subject has active lung infection or acute pulmonary decompensation.
11. Subject has elevated white blood cell count and signs of infection are evident.
12. Subject has chronic renal insufficiency as defined by serum creatinine of greater than or equal to 2 mg/dl or requirement for dialysis.
13. Subject who is pregnant or lactating or might become pregnant during the duration of the study.
14. Subject who is participating in another therapeutic interventional trial.
15. Subject has other medical, psychological, or social circumstances that may affect the ability to comply with the study requirements or increase risk to the subject.