Final answer:
The intracoronary route is used to administer cardioplegia solution to stop the heart during open-heart surgery.
Step-by-step explanation:
The cardioplegia administration route used to stop the heart during open-heart surgery is the intracoronary route. A solution of KCl, or potassium chloride, is injected into the cardiac muscle to induce cardiac arrest. This solution causes depolarization of the myocardial cells, leading to temporary cessation of the heart's pumping action.