¯Abstract Background: Synthetic drugs, although very effective, have their own side effects. Recently, herbal plants have received more attention to avoid the unpleasant effects of synthetic agents. Objective: To investigate the effects of garlic aqueous extract on contraction power of isolated atrium from male rats following administration of adrenalin. Methods: Male rats (Spirague Dawley, Albino, 200-250 gr) were divided into 7 groups as follows: Control, adrenalin, garlic extract (10 mg/kg, 20 mg/kg, and 40mg/kg), Propranolol and Propranolol plus garlic extract at a single concentration of 40 mg/kg. Later the contraction power was recorded using a physiograph set. Findings: Garlic extract at all three concentrations used in our study caused a reduction of atrial contraction power in adrenalin group. When the degree of contraction power reduction was compared between garlic extract (40mg/kg) and garlic extract plus Propranolol groups, no statistically significant difference found. Conclusion: Atrial contraction power decreased in presence of garlic aqueous extract and the degree of reduction was significant in both low and high doses, statistically.