A young motorist suffered injuries in a major road traffic accident. He was diagnosed to have a fracture of the left humerus. He also had fractures of multiple ribs anteriorly on both sides. On examination, the blood pressure was 80/60 mm Hg, and the heart rate was 140/minute. The patient was agitated, restless, and tachypneic. Jugular veins were distended. Air entry was adequate in both lung fields. Heart sounds were barely audible. Femoral pulses were weakly palpable but no pulsation could be felt distally. On a priority basis, the immediate intervention would be: