Occlusion of main pulmonary arteries can kill the patient suddenly. Occlusion of small pulmonary arteries has no major immediate effect. Occlusion of a medium-sized branch of pulmonary artery can lead to a pulmonary infarction in a person with compromised cardiac or respiratory status. A pulmonary infarct is hemorrhagic because of the dual blood supply: some blood still flows from the non-occluded bronchial arteries which mainly supply blood to interstitium, but do not prevent the infarction.