Sudden Dyspnea

An 66 year old lady who underwent an uncomplicated hemicolectomy for colo-rectal carcinoma last week is brought in complaining of sudden onset dyspnea of 2 hours duration. There is no associated fever, cough, chest pain, nausea, vomiting, faintishness or calf pain. She has no comorbidities and this is her first such episode. She does not smoke and is not on any drugs.