During open hearc surgery, cardioplegic solution iufusion is generally practiced to protectmyocardium. The main constituent of crystalloid cardioplegic solution to protect myocardiumis potassium. There are many studies of the effect of cardioplegic solution on myocardium, butstudies of the offect on coronary artery are few. To know the direct effect of the cardioplegicsolution on coronary artery, the isometric tension of rabbit coronary artery ring wag measuredduring perfusion of solutions. The results are as follows :

Crystalloid cardioplegic solutions, Y-solution and S-solution, induced contraction of oronary artery. High potassium Tyrode solution induced contraction of coronary artery. The isometric tension of coronary artery increased as the potassium concentration of the solution increases.Adenosine reduces potassium induced contraction of coronary artery in dose dependant manner, Nicardipin almost completely and persistantly abolished potassium induced contraction.Further study is needed to consider the feasibility of adding Adenosine in cardioplegic solutions.