"This Old Heart of Mine (Is Weak for You)" is a song by The Isley Brothers from 1966 that was a hit for them 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. The single was the group's only major hit while on Motown, whom they left in 1969 to restart their own T-Neck label. Tammi Terrell also recorded and released the song as a part of her Irresistible album released in January, 1969.