Pulmonary hypertension (PH) due to left heart disease, classified as group 2 according to the Dana Point 2008 classification, is believed to be the most common cause of PH and is associated with high morbidity and mortality. Epidemiological studies of group 2 PH are less exhaustive than for rarer causes of PH such as isolated pulmonary vasculopathies, but attention for this entity is growing rapidly. Group 2 PH may be caused by passive downstream elevation in left heart pressures or by a combination of the latter with pulmonary arteriolar pathologies. Improved understanding of the perturbations in pulmonary vascular structure and function that cause PH due to left heart disease is essential to reduce heart failure morbidity and mortality. In this review, epidemiology, mechanisms, diagnostic approaches, hemodynamic models, and clinical trials of heart failure complicated by group 2 PH are reviewed, along with a discussion of novel treatment strategies that are currently under investigation or hold promise for the future.