This was written by Graham Gouldman, who later formed the band 10cc. Gouldman was a prolific songwriter who also came up with songs for The Hollies, Cher, The Shadows, and Herman's Hermits. For The Yardbirds, he provided three of their hits, also composing "Evil Hearted You" and "For Your Love". It was the Yardbirds' first single after Jeff Beck replaced Eric Clapton as lead guitarist. The Yardbirds' first recorded the song with an Indian sitar player performing the distinctive instrumental figures. However, the group was dissatisfied with the results. Consequently, Beck developed the part on electric guitar using a fuzz box distortion unit. The Yardbirds' first attempt to record "Heart Full of Soul" was on 13 April 1965 at Advision Studios in London. The session began with the sitar player playing the distinctive instrumental hook or riff. However, he was unfamiliar with the type of rock sound the group was trying to achieve "It just didn't have any groove to it", Beck felt. McCarty added: "It was fine in principle, but while the tablas sounded OK, the sitar just wasn't up front enough. It just didn't cut through." Beck developed a riff on guitar to replace the sitar line. He elaborated in an interview: "The sitar player couldn't get the 4/4 time signature right; it was a hopeless waste of time. So I said, 'Look, is this the figure?' I had the fuzz machine, a Toneblender [sic], going. We did one take, it sounded outrageous. So they kept the tabla player, who could just about make it work. They rushed that out, and the rest was a rollercoaster ride." According to McCarty, Beck developed the riff after borrowing Jimmy Page's prototype fuzz box, designed for him by Roger Mayer. Page was working in an adjacent studio and attended the session. When Beck played the lick for the band, they felt that it was a perfect fit: "this great sounding riff emerged ... I mean Beck just nailed it", rhythm guitarist Chris Dreja recalled. The group returned to Advision on 20 April to complete the song. Beck was able to achieve the sitar-like hook by bending the higher notes on his guitar in an while also using his own Tone Bender unit to get the distinctive tone. While simultaneously sounding the open D string, he also added a droning quality reminiscent of the sitar's sympathetic strings. Rush practiced this a lot when they were first starting out. It is one of eight songs [Rush covered on their 30th anniversary album Feedback](https://www.invidio.us/watch?v=f9f03ZbbDM0).