"I Let a Song Go Out of My Heart" is a 1938 composition by Duke Ellington, with lyrics added by Irving Mills, Henry Nemo and John Redmond.
The song became a number one hit for Ellington in 1938.
Other hit versions the same year were by Benny Goodman (with Martha Tilton singing), Jimmy Dorsey (with June Richmond singing), Connee Boswell, Hot Lips Page, and Mildred Bailey.
[1] It was performed as part of The Cotton Club Parade of 1938.
[2] Jazz Standards