Pulmonary hypertension occurs commonly in a variety of cardiopulmonary disorders. The current classification of pulmonary hypertension is composed of five categories. Group 1, pulmonary arterial hypertension (PAH), includes idiopathic PAH, formerly called primary pulmonary hypertension, familial PAH, and PAH associated with specific medical conditions such as connective tissue diseases, congenital heart disease, and portal hypertension.1 Enthusiasm for the treatment of group 1 PAH dates back to 1995 with the US Food and Drug Administration approval of IV epoprostenol, the first specific treatment for this often fatal disease. The US Food and Drug Administration approvals of oral therapies for PAH, including bosentan (2001), sildenafil (2006), and ambrisentan (2007), have generated further interest in PAH and its treatment. However, group 1 PAH is a rare disease. In 2006, a large French Registry estimated2 the prevalence of group 1 PAH to be 15 cases per million. In reality, the most common types of pulmonary hypertension seen in practice are those in group 2, pulmonary hypertension with left heart disease, or pulmonary venous hypertension (PVH), and those in group 3, pulmonary hypertension associated with lung disease and/or hypoxemia. It is critical to differentiate both PVH and pulmonary hypertension related to lung disease from PAH, as the treatments for PAH have not been adequately studied and may in fact be detrimental in patients with these other types of pulmonary hypertension.