Pulmonary hypertension (PH) is recently defined in terms of hemodynamic criteria by a mean pulmonary arterial pressure (mPAP) determined by right heart catheterization of more than 20 mm Hg at rest. It is considered the main cause of morbidity and mortality in patients with chronic hemolytic anemias including thalassemia. It results in right ventricular failure and premature unexpected death if left untreated. PH is classified according to the World Health Organization (WHO) into five groups. Thalassemia is included within group 5 PH which occurs due to an unclear and/or multifactorial etiology. The occurrence of PH in MPNs patients has a bad impact on the prognosis of the disease and on the survival in those patients. The pathogenesis of PH in thalassemia patients is complex and multi-factorial. It is assumed to be due to multiple overlapping pathogenic mechanisms including chronic hemolysis, inflammation, oxidative stress, decreased nitric oxide (NO) bioavailability, iron overload due to frequent repeated blood transfusion, hypercoagulability, erythrocyte dysfunction due to splenectomy, and chronic tissue hypoxia resulting from anemia leading to high cardiac output state and increased pulmonary vascular resistance.