Pulmonary embolism is a very frequent disease, its diagnosis is imperative to be able to establish the proper treatment. For this purpose it is necessary to visualize the pulmonary arterial tree. Not all the defects in perfusion are produced by pulmonary embolism, then it is necessary to study the relationship between ventilation and perfusion. It is characteristic of pulmonary embolism that the ventilation is pressured and there are alterations in the pulmonary circulation. This is due to the basic physiopathology of non-complicated pulmonaryembolism which is adequate ventilation in non-perfused area. Other typical findings in non-complicated pulmonary embolism are sudden changes in the alterations of the pulmonary circulation and to find a normal chest radiography. When pulmonary embolism complicates lung disease such as a chronic obstructive lung disease the diagnosis is difficult, the chemical history is important. These studies of ventilation and perfusion can be performed with a gamma camera using Xenon133 and radioactive particles