Final answer:
The Malleable retractor is best for retracting lung lobes during heart surgery due to its flexibility and ability to be shaped to avoid injury to delicate tissues.
Step-by-step explanation:
The most appropriate retractor for use on the lung lobes to improve access to the heart is the Malleable retractor. Malleable retractors, also known as ribbon retractors, can be bent into a variety of shapes and are thus ideal for gently retracting delicate tissues such as lung tissue. Their flexibility allows surgeons to maneuver them to provide optimal exposure of the heart without causing undue pressure or injury to the lung lobes during cardiac surgery.
A retractor is a surgical instrument used to separate the edges of a surgical incision/wound or to hold away certain organs and tissues (i.e. to provide tissue retraction) so that body parts underneath may be accessed during surgical operations.