Pulmonary hypertension (PH) due to left heart disease (LHD) is the most common type of pulmonary hypertension. Pulmonary hypertension due to LHD has two subgroups: isolated post-capillary PH due to left sided filling pressures, and then in long-standing cases, the pre-capillary component is added due to pulmonary vascular disease developing, which is termed post- and pre-capillary PH. These groups have differing clinical implications. We describe the hemodynamic, from left and right heart cardiac catheterization, pathophysiology, and the role of pulmonary vasodilators and studies of this up to date. We will also discuss the left heart diseases that cause PH, such as congestive heart failure and valvular heart disease. We will also discuss future areas for research in this area of PH.