The goal of this clinical trial is to test the efficacy of tadalafil in patients with group II pulmonary hypertension with elevated pulmonary vascular resistance (PVR). The main question it aims to answer is:

• Can tadalafil improve patients with group II pulmonary hypertension with elevated PVR? Participants will undergo right heart catheterization (RHC) to make sure they are fulfilling the inclusion criteria, then will be asked to take tadalafil 20 mg for two weeks then 40 mg if tolerated for 12 weeks, then participants will be followed up. Investigators will compare the drug group with another age- and sex- matched control placebo group.

The study aims at studying the efficacy of tadalafil in patients with group 2 pulmonary hypertension with elevated pulmonary vascular resistance guided by RHC. After fulfilling the inclusion criteria, investigators will recruit 48 patients, and do baseline echocardiography for comprehensive right ventricular (RV) study and 6 minute walk test, and then start tadalafil 20 mg then 4mg if tolerated, for 24 patients (drug group). After three months follow up, investigators will follow up the patients regarding RV function and the functional capacity, compared to matched control group.

Inclusion Criteria:

• group 2 pulmonary hypertension with precapillary component with PVR more than 4 by RHC
• Patients should be on HF medical therapy 90 days before enrollment in the study.

Exclusion Criteria:

• Anticipated cardiac resynchronization therapy within 3 months of enrollment.
• Hypersensitivity, allergy, or intolerable side effects of PDE-5 inhibitors.
• Contraindication to PDE-5 inhibitors, including current nitrate therapy.
• All groups of PH, other than group 2 PH (isolated post capillary pulmonary hypertension).
• History of heart transplant, ventricular-assist device, or any other solid-organ transplant
• Likely to have solid-organ transplant or any other major surgery during study enrollment/treatment period.
• Female subject who is pregnant, breast-feeding, or unwilling to practice an acceptable method of birth control unless postmenopausal or sterile.
• Unreliability as a study participant, based on the investigator's (or designee's) knowledge of the subject (e.g., alcohol or other substance abuse, inability or unwillingness to adhere to the protocol, documented noncompliance, or vulnerable population)
• Current enrollment, or enrollment completed <30 days previously, in another investigational drug or device clinical study.
• Undergoing dialysis for end-stage renal disease.
• End-stage liver disease comorbidities, limiting exercise tolerance.
• Morbid obesity (body mass index > 40).
• Severe peripheral vascular disease with intermittent claudication.
• Status after amputation of lower extremity(s) at any level.
• Severe degenerative joint disease preventing normal walking.
• Cerebrovascular accident with long-term sequelae affecting ability to walk.