Their fourth single, the first one without Eric Clapton, who left after For Your Love, where a harpsichord took over as lead instrument. Indian sitar and tablas for Heart Full Of Soul confirmed the change of musical direction, away from the blues. Replacer Jeff Beck had no problem mastering that sitar sound on electric guitar; so convincing the Indian player engaged was set aside. The original sitar version has been released on several Yardbirds cd box sets afterwards.
Author Graham Gouldman also wrote For Your Love and Evil Hearted You for the Yardbirds, Tallyman for Jeff Beck, Bus Stop and Look Through Any Window for The Hollies, No Milk Today for Herman's Hermits, I'm Gonna Take You There for Dave Berry and Pamela Pamela for Wayne Fontana & The Mindbenders, his own band before becoming part of Hotlegs (of Neanderthal Man fame) and of course 10cc.