"My Heart Belongs to Daddy" is a song written by Cole Porter for the musical Leave It to Me! which premiered on November 9, 1938. It was originally performed by Mary Martin, who played Dolly Winslow, the young "protégée" of a rich newspaper publisher, her sugar daddy. In the musical, Dolly wears a fur coat while stranded at a Siberian railway station and surrounded by eager men. She performs a striptease and sings to them about how since she has her "daddy", she may still flirt with other men but won't "follow through".

Martin sang it again in the 1940 movie Love Thy Neighbor. Again she wears a fur coat, but the setting is a show within a show and the act is more conventional as she wears an evening gown beneath the fur. The words to the introduction are altered, the innuendoes being toned down. Her best-known movie performance is in the 1946 Cole Porter biopic Night and Day in which she plays herself. The film recreates Martin's audition then segues into her performance in the original Siberian context. She again performs the striptease, discarding her muff and then the fur coat, while mustachioed Siberian men follow her every move, eventually fainting when she removes her coat to reveal a skimpy figure-hugging costume beneath.

In Britain, the song was a hit for Pat Kirkwood, who performed it in the 1938 revue Black Velvet. This led to her being dubbed "Britain's first wartime star". The song was thereafter associated with her.

Marilyn Monroe sings the song in the film Let's Make Love (1960). The introduction is completely changed. She introduces herself as "Lolita", who is not supposed to "play with boys". A verse is added in which she invites a boy "to cook up a fine enchilada". The lines do not conform to the rhyme scheme of the rest of the song, but have been used by many other performers since. Anna Nicole Smith recorded a copy of the Monroe version in 1997; it was released in CD-single and 12 maxi with two versions.

The original has an introductory verse starting in a major key with "I used to fall in love with all" and ending by transitioning into minor while saying that she has since "come to care, for such a sweet millionaire" (i.e. her sugar daddy).

The chorus incorporates flirtatious sexual innuendo in its idiosyncratic rhymes with "daddy". While "daddy" is a difficult word to rhyme, Porter characteristically managed it well. The first rhyme is about a game of ‘stroke play’ golf during which she "might make a play for the caddy". The second rhyme suggestively refers to eating "Finnan haddie" (smoked fish):

If I invite
A boy some night
To dine on my fine Finnan haddie,
I just adore
His asking for more,
But my heart belongs to daddy.

The chorus is repeated with additional lyrics starting with a rhyme about "wearing green with a paddie" on Saint Patrick's Day and a final rhyme is about longing for a "strong undergraddy" at a football match. In the original version, she ends up saying that her daddy might "spank" her if she was "bad".