The heart is an organ especially sensitive to the sympathetic overstimulation and therefore to the influence of stressors and hypertension. The aim of the present study was to investigate the effect of two distinct types of stressors, acute immobilization (2 h) and chronic isolation stress (21 days), as well as their combined effect on the activity of monoamine oxidase (MAO), superoxide dismutase, catalase (CAT) and the ascorbic acid (AA) content in the heart of normotensive and spontaneously hypertensive rats (SHR). The results obtained show that in basal conditions heart MAO and CAT activity (p < 0.05), as well as AA concentration (p < 0.01) were higher in SHR than in normotensive ones. The acute immobilization significantly decreased heart MAO activity in both examined strains (p < 0.01). On the other hand, chronic isolation, separately or in combination with immobilization, did not affect this enzyme, in the heart of either hypertensive or normotensive rats, which was associated with the reduced antioxidative protection (p < 0.01, p < 0.05).