This chapter reviews the rationale for the use of cardioplegia, techniques of administration, components of different cardioplegia solutions and applications of cardioplegia in different surgical interventions. Myocardial damage can be detected by electrocardiography, echocardiography, radioactive imaging studies and cardiac magnetic resonance imaging. The clinical manifestations of myocardial damage may present as low cardiac output syndrome due to impaired myocardial contractility, dysrhythmias, decreased ventricular compliance or segmental myocardial wall motion abnormalities. The goal of myocardial protection with cardioplegia is to prevent myocardial injury during the periods of intentional ischemia that are required to perform cardiac operations. Cardioplegia delivery systems generally comprise an infusion system with in-line pressure monitors, a cardioplegic heat exchanger for cold and warm perfusion, and cannulae for antegrade and retrograde delivery. Crystalloid cardioplegia solutions are usually delivered at 4°C, cold blood solutions at 10-16°C and warm blood solutions at 37°C.