The purpose of the Phase 2a study is to: 1) demonstrate that the estimated VentaProst dose is safe and equivalent in effect to a dose administered via epoprostenol aerosolization by the current off-label-use practice; and 2) demonstrate that an optimum effect can be rapidly obtained with VentaProst titration.

Part I:

This part of the study is designed to demonstrate the dose equivalence between off-label aerosolized epoprostenol and VentaProst using a patient's hemodynamic parameters.

Part II:

This part of the study is designed to establish a dose response relationship of VentaProst to hemodynamic effect by dose escalation in patients who have had cardiac surgery with CPB.

Inclusion Criteria:

1. Women and Men 18 to 75 years of age

2. Provide written informed consent

3. Willing and able to comply with all aspects of the protocol

4. For patients in Part I:

   1. Undergo cardiac surgery on CPB
   2. Clinically require treatment with and receive aerosolized epoprostenol
   3. Demonstrate a clinically meaningful hemodynamic response to aerosolized epoprostenol

5. For patients in Part II:

   1. Undergo cardiac surgery with CPB
   2. Have perioperative pulmonary hypertension
   3. Clinically require treatment with inhaled epoprostenol

Exclusion Criteria:

1. Current smoker (i.e., within the last 30 days)
2. Emergency operative status
3. Upper and/or lower respiratory tract infection within four weeks of screening
4. Contraindication to transesophageal echocardiogram (TEE) including esophageal disease or unstable cervical spine
5. Renal or severe hepatic impairment
6. Thromboembolic disease treated with anticoagulant therapy
7. Bleeding disorders
8. Significant restrictive or obstructive lung disease
9. History of concurrent malignancy or recurrence of malignancy within two years prior to Screening
10. History of a diagnosis of drug or alcohol dependency or abuse within approximately the last three years
11. Recent history of stroke or transient ischemic attack
12. Significantly abnormal laboratory tests at Screening
13. Pregnant or breastfeeding
14. Treatment with an investigational drug, biologic, or device within 30 days
15. Other severe, acute, or chronic medical or psychiatric condition or laboratory abnormality that may increase the risk associated with trial participation or investigational product administration or may interfere with the interpretation of trial results and, in the judgment of the Investigator or Sponsor, would make the patient inappropriate for entry into this trial
16. Any condition where aerosolized epoprostenol is contraindicated
17. Known allergy or sensitivity to epoprostenol, any of its ingredients, or the diluent

Adverse events were collect from post-cardiac surgery (Day 1) through study completion (up to 30 days).