The aim of our study was to evaluate long-term effect (5 weeks) of Losartan (Los) and Prazosin (Pra) on blood pressure (BP), heart weight/body weight (HW/BW) and geometry of coronary artery (RS) of spontaneously hypertensive rats (SHR) and Wistar rats. We used 6 groups of 4-week-old rats: 1) Wistar rats, 2) SHR, 3) Wistar rats + Los, 4), SHR+Los, 5) Wistar rats + Pra, 6) SHR+Pra. Los (20mg/kg) and Pra (10 mg/kg) were administered orally by gavage. BP was measured by the tail plethysmographic method. After anaesthesia cardiovascular system was perfused with glutaraldehyde fixative (120 mm Hg) and RS was processed for electron microscopy. BP, HW/BW, wall thickness (WT), cross sectional area (CSA) and wall thickness/inner diameter (WD) were increased in SHR vs. Wistar rats. Los and Pra lowered BP, HW/BW of both Wistar rats and SHR. Los evoked decrease of WT, CSA, WD and increase of ID in SHR and didn't evoke changes in Wistar rats. Pra didn't evoke changes in SHR and caused increased ID and CSA in Wistar rats. Summary: both substances Los and Pra, when administered to SHR from prehypertensive period through adulthood, prevented BP increase and development of cardiac hypertrophy. Los, opposite to Pra, prevented hypertrophy of RS. Supported by VEGA 2/3145/25.