(surgery) A surgical operation on the heart while a machine keeps the blood flowing.

(transitive with to) (figuratively) To speak honestly and vulnerably about one's feelings. / To show great compassion.

plural of open-heart surgery

(figuratively) to expose problems, lies or corruption.

plural of open-top bus

(UK) A double-deck bus with an open, or partially open, top deck.

plural of open-field test

A scientific test to gauge an animal's locomotor activity levels, anxiety, and willingness to explore, by placing the animal in an enclosed arena and observing its actions.

employment contract without a set date for termination

(idiomatic) to become receptive to new ideas and perspectives