Idiopathic pulmonary arterial hypertension (formerly referred to as primary pulmonary hypertension) is an uncommon yet progressively fatal disease defined by the presence of mean pulmonary artery pressure greater than 25mmHg at rest or greater than 30mmHg with exercise as tested by right heart catheterization in the absence of other etiologies for pulmonary hypertension. Across several studied populations, the diagnosis takes an average of 2.0 to 2.9 years to make, because its initial symptoms are minimized by patients and are characteristic of other, more common disorders. Diseases such as connective tissue diseases, chronic thromboembolic disease, congenital heart defects, chronic hypoxia, left ventricular dysfunction, portal hypertension, and HIV, as well as exposures to anorexigens, methamphetamines, and cocaine have also been found to have disease- and toxinassociated pulmonary arterial hypertension (PAH). Physical exam and first-line diagnostic studies such as electrocardiograms (ECGs) and chest radiographs often show subtle differences compared with normal patients. Patients are stratified according to symptoms based upon the modified New York Heart Association (NYHA) classification, also referred to as the World Health Organization (WHO) functional classification, as these strata have mortality implications. Untreated patients in class I and II have a median survival of nearly six years compared with untreated patients in class III, who have a median survival of 2.5 years, and untreated patients in class IV who have a median survival of six months. Note that according to the WHO classification, the presence of syncope independently places pulmonary hypertension patients into class IV, unlike patients who have congestive heart failure. Patients’ clinical course can be followed invasively with routine right heart catheterizations or non-invasively through six-minute walk testing, or newer modalities such as cardiac computed tomography (CT) or cardiac magnetic resonance imaging (MRI). An expert panel from the American College of Chest Physicians (ACCP) has developed an algorithm from their 2004 guidelines to help clinicians navigate through the myriad diagnostic tests to make the correct diagnosis.