Keritot, Chapter Six, Mishnah Seven
This mishnah contains some rules governing the hatat.
1) If a man set aside his hatat and then died, his son should not offer it after him.
2) A man may not offer [what was set apart] for one sin for another sin.
a) Even if he had set apart [the hatat] for forbidden fat that he had eaten yesterday, he may not offer it for forbidden fat that he has eaten today, for it is said, His offering … for his sin (Leviticus 4:28)the offering must be for that particular sin.
Section one: If the owner of a hatat has died, the animal cannot be offered, not even by his son. Rather, it must be left to die (see Temurah 2:2).
Section two: If an animal was set aside to be a hatat for one sin, he cannot offer it for another sin, even if it is the same sin, such as eating helev. This is derived from a midrashic reading of Leviticus 4:28.