The aim of this research was to evaluate the possible protective effect of pravastatin on ultrastructural alterations induced by cold stress in the myocardium of rats. Sixteen EPM-Wistar rats (Rattus norvegicus albinus) were used and distributed into four groups: 1) control; 2) pravastatin; 3) cold stress, and 4) pravastatin + cold stress. A daily oral dose of 10 mg/kg of weight of pravastatin was administered to each rat in groups 2 and 4 for 15 days. The stress induced by cold was obtained by keeping the group 3 and 4 rats in a freezer at -8 degrees C for 4 hours. The animals were killed and the heart and fragments of the left ventricles (LV) were removed and processed prior to conducting electron microscopic analysis. The ultrastructural alterations in cardiomyocytes were quantified through the number of mitochondrial cristae pattern (cristalysis). The group subjected only to cold stress showed a significant increase in cristalysis (391.9) when compared with control group (42.0). In the cold stress and pravastatin pretreatment group, a statistically significant (96.9)*, P<0.05 cristalysis reduction was observed when compared with cold stress group. The mitochondrial cristalysis profiles of the control and pravastatin groups were 42.0 and 65.7, respectively. Cold stress induced a significant increase in the rate of mitochondrial cristalysis. In the group that received pravastatin and was exposed to cold stress, the drug protected the LV cardiomyocytes. This fact was confirmed by a reduction mitochondrial cristalysis pattern.