Those factors that prolong myocardial tolerance to global ischemia constitute an important prerequisite for effective cardioplegia. This study contrasts the relative buffering power of bicarbonate-based and tromethamine-based hyperkalemic crystalloid cardioplegic solution with histidine protein-type buffer (Bretschneider) solution. In addition, the solutions were compared with titration of whole blood and myocardial muscle homogenate.