Experiments were carried out to provide further information on the biochemical and morphological changes occurring in the guinea-pig heart after multiple ligature and reopening of the left anterior descending (LAD) coronary artery. In isolated perfused guinea-pig heart the reopening of LAD coronary artery leads to a release of histamine related to a loss of metachromasia by cardiac mast cells. The process is associated with malonyldialdehyde (MDA) production, cellular overload of calcium and ventricular arrhythmias which can be modulated by pharmacological interventions.