Pulmonary embolus is known as a Great Masquerader for the nonspecificity of symptoms and inconclusiveness of diagnostic tests. The annual incident in the United States alone is about 600,000 with 50,000 to 200,000 of those people dying. With rapid recognition and treatment, mortality and morbidity rates can be significantly improved. Most pulmonary emboli are diagnosed at autopsy, making this a subject needful of careful consideration during evaluation of any patient. Knowing how to interpret diagnostic tests and which are the most cost effective with the greatest specificity enhances the practitioner's ability to rapidly diagnosis or rescue patients.