Pulmonary embolism: classically pleuritic chest pain, dyspnea +/- hemoptysis; often subtle presentation with unexplained hypoxia, tachycardia, tachypnea; decreased SpO2; signs: swollen legs and unilateral leg pain, erythema (DVT), sinus tachycardia, risk factors - Virchow's triad (flow stasis e.g. immobilization or surgery, hyper-coagulability e.g. cancer, pregnancy, endothelial damage e.g. vasculitis, stroke)