A twenty-two year old female in her third trimester of pregnancy was involved in a motor vehicle accident. She was belted. Paramedics report the patient was alert and oriented and her vital signs were stable. In the ER, she complains of pain on the left rib cage and shortness of breath. Physical examination is significant for increased jugular venous pressure, hypotension, and paradoxical pulse of 20 mmHg. EKG monitoring shows amplitude change with her heart beat (electrical alternans).