If both parties are cis and identify as male and female, it is a hetero relationship. A hetero relationship could do things to queer their relationship (queer as a vreb, here), like be open to each other sleeping with others, or others of same cis genders, or strap on analysis sex, etc.

my dad identifies as bi, and was sexual active in the gay community before I was born. He's only been in 4 relationships since I was born, all with cis women. He still identifies as bi, but he is in a hetero relationship.