Final answer:
Ethylene oxide is the agent used to sterilize the plastic tubing of heart-lung machines. It is a gaseous sterilant that can penetrate heat-sensitive materials like plastic tubing.
Step-by-step explanation:
Ethylene oxide is an agent that is used to sterilize the plastic tubing of heart-lung machines. It is a gaseous sterilant that can penetrate heat-sensitive materials like plastic tubing. However, caution must be exercised as ethylene oxide is highly explosive and carcinogenic.