Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Pulmonary embolism is a common condition which occurs when the main artery of the lung gets blocked by a substance, usually a blood clot, that has reached the lung through the bloodstream. Although in most cases blood clots in the main artery are not life threatening, medics remind that pulmonary embolism is a potentially lethal condition, massive pulmonary embolism being the second leading cause of sudden death. Learn more about pulmonary embolism, its causes, symptoms and treatment in this book.