AbstractThe aortic valve was investigated in 58 sheep and 60 swine without heart disease. After fixation in 4% formalin, the distance between the ostia and the elements of the right/left aortic sinuses was measured. For the left coronary ostium (LCO), it was found that in sheep 81% were below and 19% at the level of intercomissural line (IL). In pigs, 88.3% were below and 11.7% at the IL level. In sheep, the OCL was close to the right valve commissure (CVR) in 98.3% and close to the left valve commissure (CVV) in 1.7%. In pigs, it was close to RVC at 83.3% and close to LVC at 16.7%. Regarding to RCO, it was found that in sheep 69% was below, 1.7% was above and 29.3% at the IL level. In pigs, 20% were below, 15% above and 65% at the IL level. The distance of the RCO in relation to the valve commissures was 56.9% close to LVC and 43.1% close to RVC in sheep. In pigs, 81.7% were close to LVC and 18.3% close to RVC. The position of LCO was balanced between sheep and swine, while the RCO in swine was closer to CVE when compared with sheep. The accessory coronary ostium was observed in 18.6% of sheep and 10% of pigs. Thus, it is concluded that in sheep and swine the left coronary artery is perfused only in ventricular diastole. Perfusion of the right coronary artery occurs more frequently in diastole and less frequently in ventricular systole.