A Study to Evaluate the Efficacy, Safety and Tolerability of PDNO Infusion in Patients With Pulmonary Hypertension After Cardiopulmonary Bypass Surgery

Inclusion Criteria: * Ability to understand and willing to sign an informed consent form (ICF) * Male and female patients, age ≥ 18 years * Planned to undergo elective cardiopulmonary bypass (CPB) for coronary artery bypass grafting (CABG), aortic valve repair (AVR) or mitral valve repair (MVR) with or without CABG * Diagnosed with echocardiographic signs of pulmonary artery systolic pressure (PASP) \>50 mmHg , as estimated by doppler defined echocardiography using a modified Bernoulli equation: PASP ≈ 4 (tricuspid regurgitant jet velocity)\^2 + central venous pressure (CVP) Exclusion Criteria: * History of chronic pulmonary hypertension (PH) (WHO group 1, 3, 4 or 5), not group 2 due to left heart disease * Patients with contraindications for pulmonary artery catheter (PAC) * History of severe chronic obstructive pulmonary disease * Left heart failure with ejection fraction (EF) \<35% * Non-ST elevation myocardial infarction (non-STEMI) or ST elevation myocardial infarction (STEMI) within 1 months prior to informed consent * Stroke (cerebrovascular lesion \[CVL\]), transient ischemic attack (TIA), AV block III within 3 months prior to informed consent or QTcF \>450ms at the time of screening * High inotropic requirement (no more than one inotrope treatment and the vasopressor norepinephrine at time of screening/postoperative evaluation) * (Increased) mediastinal bleeding \>100 mL/hour in mediastinal drainage at postoperative evaluation * Mechanical circulatory assistance (intra aortic balloon pump \[IABP\] or right/left-ventricular assist device \[R/L VAD\]) * Echocardiographic evidence of significant tricuspid insufficiency * Body Mass Index (BMI) \>40 kg/m\^2 * Estimated glomerular filtration rate (eGFR) \< 30 mL/min preoperative value * Methemoglobin \>3% * Indication of liver disease, defined by serum levels of either alanine aminotransferase (ALT), aspartate aminotransferase (AST) or alkaline phosphatase (ALP) above 3 x upper limit of normal (ULN) (preoperative value) * Preoperative haemoglobin \<10 g/dL, postoperative: Hb \< 9 g/dL * Thrombocytopenia (platelet count \<100,000/mm\^3), preoperative value * Prothrombin time International ratio (INR) \> 1.3, preoperative value * Pregnant or lactating women, or with a positive pregnancy test at screening (for fertile women only) * Ongoing daily treatment the last 3 days with non-steroidal anti-inflammatory drugs (NSAIDs, excluding low dose, i.e. 75 mg, acetylsalicylic acid), new oral anticoagulants (NOACs), warfarin, heparin, clopidogrel (last 5 days). Low molecular weight heparin (LMWH) is not an exclusion criterion. Any use of PDE5 inhibitors (sildenafil, tadalafil, vardenafil and avanafil) within 48 hours prior to the administration of PDNO. * Known active malignancy within the past 3 years except for localized prostate cancer, cervical carcinoma in situ, breast cancer in situ, or nonmelanoma skin cancer that has been definitively treated * History of allergy/hypersensitivity to PD or ongoing allergy/hypersensitivity or history of hypersensitivity to drugs with a similar chemical structure or class to PDNO * History of any other clinically significant disease or disorder * Participation in any interventional clinical study or has been treated with any investigational research products within 30 days or 5 half-lives, whichever is longer, prior to the initiation of screening