We describe a patient with myelofibrosis, giant splenomegaly, and pulmonary hypertension related to increased intra-abdominal pressure. Focusing on alterations in hemodynamic studies, we conclude that in patients with myelofibrosis, dyspnea, and hypoxemia, the measurement of intra-abdominal pressure should be included in the initial evaluation. It is an inexpensive, non-invasive diagnostic tool that can provide crucial information about the cause of dyspnea and disclose the pathogenetic link between massive splenomegaly and pulmonary compromise in myelofibrosis. Am.