The patient is presenting with dyspnea and tachpnea;dyspnoea with hypotension(BP:90/60 mmHg) indicates a massive pulmonary embolism.He is also presenting with a classic sign of PE,i.e.,an accentuated pulmonic component of the second hea sound.The most sensitive test for PE is D-dimer ELISA assay which rises due to the breakdown of fibrin by plasmin.The most frequently cited abnormality in ECG,in addition to sinus tachycardia ,is the S1Q3T3 sign-an S wave in lead I,a Q wave in lead III,and an inveed T wave in lead III.This finding is relatively specific.The gold standard test for PE is CT pulmonary angiography.On confirming the diagnosis ,primary therapy consisting of clot dissolution with thrombolytics like tPA/streptokinase or removal of PE by embolectomy is done.Anticoagulation with heparin and warfarin or placement of an inferior vena caval filter constitutes secondary prevention. Reference:Harrison's medicine-18th edition,page no:2172-2177.