Greenwich died of a heart attack at St. Luke’s Roosevelt Hospital, where she had been admitted a few days earlier for treatment of pneumonia, according to her niece, Jessica Weiner.

Greenwich, a member of the Songwriters Hall of Fame, was considered one of pop’s most successful songwriters. She had a rich musical partnership with the legendary Phil Spector, whose “wall of sound” technique changed rock music. With Spector, she wrote some of pop’s most memorable songs, including “Da Doo Ron Ron” and “River Deep, Mountain High.” But Spector wasn’t her only collaborator.

She also had key hits with her ex-husband Jeff Barry, including the dynamic song “Leader of the Pack” (years later, Broadway would stage a Tony-nominated musical with the same name based on her life).

“He was the first male I could actually harmonize with,” she once said.

Greenwich was a native of Brooklyn. While she garnered her greatest success as a songwriter, Greenwich started out as a performer. She performed in talent shows as a child, and by the time she was a teen, she had her own group, called The Jivettes.

She went to college, where she met Barry, and shortly after graduation, began working for songwriters Jerry Leiber and Mike Stoller, where she got her break. She had her first chart success with the Jay and the Americans song “This Is It,” which she wrote with Doc Pomus and Tony Powers.

She also had success with Barry as the duo The Raindrops with the songs “What a Guy” and “The Kind of Boy You Can’t Forget.”

Greenwich also worked as an arranger and singer, a role that saw her working with artists including Frank Sinatra and Ella Fitzgerald.

She is also credited with helping Neil Diamond get his start and was a co-producer of early Diamond hits “Cherry, Cherry” and “Kentucky Woman.”

“Ellie Greenwich was one of the most important people in my career. She discovered me as a down-and-out songwriter and with her then-husband Jeff Barry co-produced all my early hits on Bang records,” said Diamond in a statement. “She has remained a great friend and mentor over the years and will be missed greatly.”

Among the more famous songs she wrote are “Baby I Love You,” ”Do Wah Diddy Diddy” and “Look of Love.”

Greenwich is survived by a sister, brother-in-law, nephew and her niece.