en Cardiovascular Physiology/Pharmacology Cardiovascular Physiology/Pharmacology Experimental research article Experimental research article Introduction: Inhibition of renin angiotensin system represents an important approach in the management of cardiovascular diseases. The aim of this study was to explore the effects of pretreatment with non-hypotensive dose of angiotensin converting enzyme (ACE) inhibitor, ramiprilat and angiotensin type 1 (AT1) receptor blocker, losartan on myocardial infarct size and arrhythmias in a rat model of ischemia-reperfusion injury. Methods: Seventy male Wistar rats were divided into five groups. One group received saline as control. Other groups were given 10 mg/kg/day of losartan for one (L-1W) or ten weeks (L-10W) as well as 50 μg/kg/day of ramiprilat for one (R-1W) or ten weeks (R-10W) using a feeding needle. The rats were subjected to 30 minutes occlusion and 120 minutes reperfusion of the left coronary artery. Infarct size was determined using triphenyl tetrazolium chloride staining. Ischemia-induced ventricular arrhythmias were analyzed in accordance with the Lambeth conventions. Results: Myocardial infarct size and the number of ventricular beats were significantly reduced in R-1W group, but the reduction was not significant in L-1W. After increasing the duration of pretreatment to 10 weeks in L-10W group, the infarct size, the number of ventricular beats and the episodes of ventricular tachycardia were significantly decreased. However in R-10W group the reduction of ventricular arrhythmias was not significant Conclusion: Based on the above mentioned results it could be concluded that losartan and ramiprilat, at a nonhypotensive dose, can reduce the induction of arrhythmias and infarct size following myocardial ischemia reperfusion. These drugs appear to act in a time-dependent manner. Therefore, we expected an increased cardiac effect by long-term administration of losartan. However prolonged treatment with ramiprilat reduced its protective effect. Ischemia-Reperfusion Injury, Infarct, Ramiprilat, Losartan, Arrhythmia 116 123 http://ppj.phypha.ir/browse.php?a_code=A-10-494-1&slc_lang=en&sid=1 Fatemeh Safari fa.cardio@gmail.com 320031947532846008901 320031947532846008901 No Sohrab Hajizadeh hajizads@modares.ac.ir 320031947532846008902 320031947532846008902 Yes Shahnaz Shekarforush sh.shekar@yahoo.com 320031947532846008903 320031947532846008903 No Mehdi Forouzandeh 320031947532846008904 320031947532846008904 No Mohsen Foadoddini foadmohsen@yahoo.com 320031947532846008905 320031947532846008905 No Gholamreza Bayat gbayat2005@yahoo.com 320031947532846008906 320031947532846008906 No Bita Houshmand b_hooshmand@modares.ac.ir 320031947532846008907 320031947532846008907 No Ali Khoshbaten a.khoshbaten@bmsu.ac.ir 320031947532846008908 320031947532846008908 No