A Study to Learn About the Study Medicine Called PF-07868489 in Healthy Adult People and in People With Pulmonary Arterial Hypertension

Key Inclusion Criteria Part A:

• overtly healthy
• Body mass index (BMI) of 16 to 32 kg/m2; and a total body weight >50 kg.

Key Exclusion Criteria Part A:

• clinically significant hematological, renal, endocrine, pulmonary, gastrointestinal, cardiovascular, hepatic, psychiatric, neurological, infections or allergic disease.
• smoking more than 10 cigarettes (or equivalent) per day or smoking history ≥10 pack-years.

Key Inclusion Criteria Part B:

• diagnosis of pulmonary arterial hypertension (PAH)
• stable dose of standard of care PAH vasodilators
• BMI 16 to 40 kg/m2; and a total body weight >45 kg.
• 6MWD ≥ 150 and ≤ 450.
• Pre-randomization RHC documenting a minimum of PVR ≥ 400 dyn ∙sec/cm5.

Key Exclusion Criteria Part B:

• Any medical or psychiatric condition or laboratory abnormality.
• Stopped receiving pulmonary hypertension chronic general supportive therapy 90 days prior to Day 1.
• Pulmonary capillary wedge pressure > 15 mmHg on right heart catheterization (RHC) conducted during Screening.
• History of severe allergic or anaphylactic reaction or hypersensitivity to recombinant proteins or excipients in investigational product.
• Major surgery within 8 weeks prior to randomization.
• Participants who smoke more than 10 cigarettes (or equivalent) per day or has a smoking history ≥10 pack-years.