Heart failure is the most common cause of pulmonary hypertension. Pulmonary vascular resistance is often increased in patients with left ventricular failure as a result of the breakdown of vascular smooth muscle tone and structural remodeling. Pulmonary hypertension is defined as a mean pulmonary artery pressure above 25 mm Hg at rest or 30 mm Hg during exercise. Pulmonary hypertension in heart failure is known as venous or postcapillary pulmonary hypertension. The main feature that differentiates pulmonary hypertension from pulmonary hypertension secondary to heart failure is increased pulmonary capillary wedge pressure that is present in heart failure and pulmonary hypertension absent. Although it is related to left heart failure, pulmonary hypertension that occurs in the context of heart failure does not seem to correlate with the severity of left ventricular systolic dysfunction. Diagnostic approach of pulmonary hypertension due to left heart failure is similar to that of pulmonary arterial hypertension. Doppler echocardiography is the best screening method. In patients with heart failure, pulmonary hypertension is a predictor of poor prognosis and is associated with increased long-term and short-term mortality not only in patients with systolic heart failure, but also in those with preserved ejection fraction. Currently, there is no specific therapy for pulmonary hypertension due to left heart failure. Pulmonary hypertension due to left heart failure can be improved after treatment that improves left ventricular function. The conventional treatment of heart failure, including ACE inhibitors, beta blockers, digoxin, and most vasodilators, reduces pulmonary vascular resistance. Beta-blockers, which normally do not affect pulmonary pressure, may improve pulmonary hypertension, by improving left ventricular function. Cardiac resynchronization therapy increases cardiac output and lowers pulmonary capillary wedge pressure, thus reversing hemodynamic abnormalities that have led to secondary pulmonary hypertension in patients with heart failure. Many drugs used to treat pulmonary arterial hypertension are tested for treatment of pulmonary hypertension in heart failure. Long-term benefits of these therapies are not yet known. Randomized clinical trials of endothelin antagonists and prostaglandins were not targeting patients with heart failure and pulmonary hypertension and therefore are not conclusive.