The importance of obtaining normal values of ST-segment for specific breeds of animals besides the high variability of indices in small ruminant has been emphasized. The animals were assigned into 4 groups (G1-4), according to their age: G1<3 months, 3 months ≤G2< 1 year, 1 year≤G3<3 years, and G4 ≥ 3 years old. There were 34 animals in each study group. The animals were assigned to two comprising groups: sheep, goat, male and female. Also, the animals were divided into three groups according to their breed, including: Kermani sheep, Saanen and Cashmere (Raini) goats. The present study showed that sex, age and breed had no effect on ST-segment in sheep and goats and the obtained data can provide a good basis for judging the ST-segment length and morphology in difference sexes, breeds and age groups of sheep and goats.