The purpose of this study is to

• Determine blood peptide levels and investigate any tissue gradients of apelin in patients with idiopathic pulmonary arterial hypertension and healthy volunteers.
• Evaluate the effect of exogenous apelin infusion on exercise performance in healthy volunteers and patients with idiopathic pulmonary arterial hypertension.

Idiopathic pulmonary arterial hypertension remains an enigma for physician in both diagnosis and treatment. Existing biomarkers, tissue characteristics and definite treatment are restricted. There are many evidences suggested that Apelin-APJ system associated with Idiopathic Pulmonary Arterial Hypertension (IPAH). A comprehensive characterise circulating peptide levels and investigate any tissue gradients of apelin in patients with idiopathic pulmonary arterial hypertension and healthy volunteers might provide important information about pathophysiologic process and diagnostic marker. In addition, first time human study to assessment the effect of exogenous apelin infusion on exercise performance in healthy volunteers and patients with idiopathic pulmonary arterial hypertension is essential to confirm whether the relevance between animal models and clinical subjects.

Inclusion Criteria for Control group:

• Structurally normal heart by 2D Echocardiography
• Pulmonary artery pressure < 25mmHg
• Tricuspid velocity < 2.5ms-1

Inclusion Criteria for Treatment group:

• Clinical diagnosis of Pulmonary arterial hypertension that is idiopathic, associated with anorexigens associated with connective tissue disease or familial
• Able to give informed consent
• Mean pulmonary artery pressure > 25mmHg, pulmonary capillary wedge pressure < 15mmHg, with normal or reduced cardiac output.

Exclusion Criteria for ALL group:

• Bleeding diathesis (PT > 14 sec to aPTT > 40 sec)
• Pregnancy, or women of child bearing potential not on adequate contraception
• Renal or hepatic failure
• Severe valvular heart disease
• Left ventricular dysfunction (LVEF < 40)
• Chronic lung disease
• Malignant arrhythmias
• Chronic thromboembolic disease