The magnitude of embolic obstruction by pulmonary angiographic studies has been shown to be directly related to the hemodynamic status after pulmonary embolism in patients free of prior cardiopulmonary disease; however, in patients with prior cardiopulmonary disease, the hemodynamic status after embolism may be determined either by the preembolic hemodynamic status, the magnitude of embolic obstruction, or both. No reliable index has been available to help determine the relative roles of embolism and preembolic hemodynamic disturbances in the postembolic hemodynamic status. The present study suggests that the ratio of the mean pulmonary arterial pressure to the pulmonary angiographic obstruction may effectively distinguish those patients in whom pulmonary embolism is the primary determinant of the postembolic hemodynamic abnormality from those in whom the preembolic hemodynamic abnormalities play the dominant role.