Male and female rats were exposed to noise 6 h daily for 7 days running and the effect of stress was evaluated both on myocardium ultrastructure and plasma corticosterone level. Both sexes showed subcellular alterations of cardiomyocytes; mitochondria, in particular, which resulted the most affected organelles, exhibited diluted matrix and cristolysis; in some areas, the sarcoplasmic reticulum appeared vesiculated. Quantitative analysis of altered mitochondria revealed that atrial myocardium was more affected in males than in females. Moreover, corticosterone plasma assay showed, in exposed animals, a growing increase without significant gender differences. The present findings suggest a more marked involvement of male sex when challenged with noise stressor.