Heterosexuality is an opposite sex attraction. Gender is irrelevant for these terms.
Definition of Heterosexual
Medical Author: William C. Shiel Jr., MD, FACP, FACR
Heterosexual: A person sexually attracted to persons of the opposite sex. Or a person who has sexual relations with the opposite sex. Colloquially known as "straight."
heterosexual [het″er-o-sek´shoo-al] >1. pertaining to, characteristic of, or directed toward the opposite sex. >2. a person with erotic interests directed toward the opposite sex.
https://medical-dictionary.thefreedictionary.com/Heterosexual
Medical Definition of heterosexual (Entry 1 of 2)
1a: of, relating to, or characterized by sexual or romantic attraction to or between individuals of the opposite sex b : of, relating to, or involving sexual activity between individuals of the opposite sex
sexual relationships between individuals of opposite sexes are heterosexual — A. C. Kinsey
2: of or relating to different sexes
https://www.merriam-webster.com/dictionary/heterosexual#medicalDictionary
Heterosexuality: The sexual attraction or relationship between members of the opposite sex.
U.S. National Library of Medicine
Heterosexual: A person who is attracted to members of the opposite sex
University of Cambridge LGB&T Glossary
Heterosexual or straight — attracted to people of the opposite sex.
Louisiana State University LGBTQ+ Project
https://www.lsu.edu/lgbtqproject/resources/vocabulary.php
Heterosexual/Straight = (of a person) sexually attracted to people of the opposite sex.
Cal Poly Pomona Pride Center
https://www.cpp.edu/~oslcc/pride/common-lgbtq-terminology.shtml
Heterosexual = sexually attracted to people of the opposite sex
Health Direct, Australian Government Department of Health
Straight: attracted to people of the opposite sex
University of Pittsburgh Medical Center (UPMC) Children’s Hospital of Pittsburgh
Heterosexual: sexually attracted to people of the opposite sex
Cambridge Dictionary
Heterosexual, Straight: a person who is physically, romantically, emotionally and/or sexually attracted to people of the opposite sex.
Southern Utah University Pride Alliance
Heterosexual: A clinical term for someone having emotional, physical, and sexual responses primarily to members of the opposite sex. Slang: “straight”.
Fort Lewis College
Heterosexuality: Sexual, emotional, and/or romantic attraction to a sex other than one's own. Individuals identifying as heterosexual are also referred to as "straight."
Muhlenberg College
Heterosexual – someone who is attracted to people of the opposite sex (more commonly known as “straight”)
Brookhaven National Lab Pride Alliance
Heterosexual: A person’s sexual orientation/attraction towards the opposite sex
Devon County Council, Diversity Guide - Sexual Orientation
We can do the same thing with "homosexual" and the results will show it to be a same sex attraction.
Gay and lesbian people discover that they are attracted to people of the same sex, just as heterosexuals discover that they are attracted to people of the opposite sex. The attraction appears to be the result of biologic and environmental influences and is not a matter of choice. Therefore, the popular term “sexual preference” makes little sense in matters of sexual orientation, whether the orientation is heterosexual, homosexual, or bisexual.
https://www.merriam-webster.com/dictionary/homosexual#usage-1
Definition of homosexual (Entry 1 of 2)
1now sometimes disparaging + offensive, see usage paragraph below : of, relating to, or characterized by sexual or romantic attraction to people of one's same sex : GAY
2now sometimes disparaging + offensive, see usage paragraph below : of, relating to, or involving sexual activity between people of the same sex
https://www.oxfordlearnersdictionaries.com/us/definition/english/homosexual_1?q=Homosexual
homosexual adjective
/ˌhəʊməˈsekʃuəl/, /ˌhɒməˈsekʃuəl/
/ˌhəʊməˈsekʃuəl/
>sexually attracted to people of the same sex; showing this
a homosexual act/relationship
COMPARE bisexual, gay (1), heterosexual, lesbian
GENDER IS IRRELEVANT.