The mechanism of action, characteristics and components, dosage and administration, and adverse effects of cardioplegia solution are described. The pharmacist's role in the formulation, preparation, and quality control of cardioplegia solution is also discussed. The use of cardioplegia solution has substantially increased the safety of cardiac surgery. It protects the myocardium by inducing a rapid and complete diastolic arrest, minimizing myocardial energy requirements and preventing ischemic damage during the arrest phase, and minimizing or preventing reperfusion injury once coronary blood flow is restored. Chemical components added to the cardioplegia solution, such as potassium and glucose, are largely responsible for this protective effect. Basic characteristics of cardioplegia solutions include temperature, osmolarity, and pH. Crystalloid solution has traditionally been used as a vehicle for cardioplegia solution; however, laboratory and clinical studies have demonstrated favorable effects of blood-based cardioplegia solution. Single-pass and recirculating delivery systems can be used to administer either crystalloid or blood cardioplegia solutions. Pharmacists can play a major role in the formulation, preparation, distribution, and quality control of cardioplegia solutions; these solutions prevent myocardial injury during the arrest and reperfusion phases of cardiac surgery.