Heart Theory (stylized in all lowercase[1]) is the fifth studio album recorded by Canadian singer and songwriter Lindsay Ell.

[2] The track listing for Heart Theory goes through the seven stages of grief in order, as follows: shock ("Hits Me"), denial ("How Good" and "I Don't Love You"), anger ("Want Me Back", "Get Over You", and "Wrong Girl"), bargaining ("Body Language of a Breakup"), depression ("Good on You"), testing ("The Other Side" and "Go To"), and acceptance ("Make You" and "Ready to Love").

[8] American Songwriter wrote that Heart Theory was a "career-altering, masterpiece of an album" that takes "rising artist" Ell "into legendary territory.

"[9] Mae Trumata of The Upcoming rated the album three stars out of five and wrote that the relatable nature of the songs was a "double-edged sword... that downplays Ell and her music's individuality.

"[10] In the United States, Heart Theory failed to enter the Billboard 200 but did debut at number 53 on the Top Album Sales component chart.