Acute Dyspnea has a wide differential diagnosis from Metabolic Acidosis to Medically Unexplained Dyspnea. As a bonus to Episode 21 on Pulmonary Embolism and Acute Dyspnea, Dr. John Foote the CCFP(EM) residency program director at the University of Toronto presents his Best Case Ever related to an Acute Dyspnea presentation. In the related episode on Pulmonary Embolism we havet, with Dr. Foote, the triumphant return of Dr. Anil Chopra, the Head of the Divisions of Emergency Medicine at University of Toronto . We kick it off with Dr. Foote’s approach to undifferentiated acute dyspnea and explanation of Medically Unexplained Dyspea (‘MUD’) and go on to discuss how best to develop a clinical pretest probability for the diagnosis of pulmonary embolism using risk factors, the value of the PERC rule, Well’s criteria and how clinical gestalt plays into pretest probability. Dr. Chopra tells about the appropriate use of D-dimer to improve our diagnostic accuracy without leading to over-investigation and unwarranted anticoagulation. We then discuss the value of V/Q scan in the workup of PE, and the pitfalls of CT angiography. A discussion of anticoagulation choices follows and the controversies around thrombolysis for submassive PE closes the podcast.