Inclusion Criteria:  Subjects must meet all of the following inclusion criteria to be eligible for enrollment into the trial:  Age ≥ 18 years' old Diagnosis of CTEPH Not a candidate for PTE Candidate for BPA based on suitable anatomy and disease burden Treatment-naïve (no CTEPH or pulmonary arterial hypertension (PAH)-specific medical therapies) with plans for initiation of CTEPH/PAH-specific medical therapy and treatment with BPA. Willing and able to give informed consent and adhere to visit/protocol schedules (Consent must be given before any study procedures are performed).  Exclusion Criteria:  Subjects presenting with any of the following will not be included in the trials:  Moderate to severe heart disease (LVEF < 45% or severe LV Hypertrophy) Sarcoidosis Active cancer Sickle cell anemia Liver disease (Childs-Pugh class C) Prisoners Pregnant, planning pregnancy or lactating Conditions that will prohibit MRI scanning (metal in eye, claustrophobia, inability to lie supine) Contraindication to riociguat or macitentan Medical or psychological conditions which, in the opinion of the investigator, might create undue risk to the subject or interfere with the subject's ability to comply with the protocol requirements