"This Old Heart of Mine (Is Weak for You)" is a Holland–Dozier–Holland song that was a hit for American musical group the Isley Brothers in January 1966 during their brief tenure on Motown's Tamla label. Featuring Ronald Isley on lead vocal, "This Old Heart of Mine" peaked at number twelve on the Billboard Hot 100, and at number six on the Billboard R&B Singles chart. In the UK, the song originally reached number 47 in April 1966, but it re-charted in late 1968 and reached number three for two weeks in November, making it the group's highest charting UK single.