INTRODUCTION: Pharmacological cardioplegic solution aims to eliminate the consequences of ischemic damage, which results from the misbalance between the offer and consumption of energy during the arrest of the heart beats during cardiac surgery with cardiopulmonary bypass. OBJECTIVES: This research experimentally evaluates the structural and ultrastructural changes in isolated rabbit hearts submitted to arrest protected by a Low Volumetric Cardioplegic Solution (LVCS). MATERIAL AND METHOD: The study counted with a control group and two experimental groups. In group I the cardiac arrest was obtained by infusion of the LVCS for 2 hours. In group II the experiment was conducted in the same way until the arrest protected by LVCS for 2 hours, and immediately after reperfusion was performed with the Ringer Locke (RL) oxygenated solution for 1 hour. In the control group the hearts were perfused with the RL oxygenated solution for 2 hours. After the experiments, 8 samples of the left ventricle were fixed in 10% formaldehyde and 2.5% glutaraldehyde for histological and ultrastructural analysis. RESULTS: The myocardial cells, the fibroblasts and the endothelial cells which were observed in the experimental groups I and II, presented with marginalization of the heterochromatin, compaction of the nucleolus, change in the morphology of the mitochondria and compaction of the cristae. Also there was an increase of the density of the mitochondrial matrix. This indicates that the nuclear structure as well as the structure of the cytoplasmic organelles were altered when compared to the cells of the control group. CONCLUSION: The structural modifications were due a physiological adaptation of the cell, and not an indication of oncosis or apoptosis, suggesting that the cardioplegic solution used was efficient for the preservation of the cells.
