Written by Graham Gouldman, it was the Yardbirds' first single after Jeff Beck replaced Eric Clapton as lead guitarist.

Released only three months after "For Your Love", "Heart Full of Soul" reached the Top 10 on the singles charts in the UK, US, and several other countries.

Inspired in part by the addition of guitarist Jeff Beck, who replaced Clapton, the group began to experiment with different musical styles.

[6][7] Music critic Richie Unterberger described Gouldman as "a genius at effectively alternating tempos and major/minor modes", as used in "Heart Full of Soul".

[7] Beck biographer Martin Power says that "For Your Love" had been made more memorable by a prominent harpsichord part (played by Brian Auger) and that may have influenced Gomelsky's decision.

[3] Beck also believes that the addition of an unusual instrument was an attempt to follow the successful incorporation of a harpsichord in their first hit.

[9]According to McCarty, Beck developed the riff after borrowing Page's prototype fuzz box, designed for him by Roger Mayer.

[2][3] Music writer Alan di Perna describes it as "microtonal string bending", while Relf biographer David French calls Beck's sound a "violin-like fuzz".

[3] Beck's contribution was described in a June 1965 single pre-release review in Beat Instrumental as providing an "oriental touch"[4][b] and it was seen as helping to introduce "the psychedelic subgenre known as 'raga rock'", according to di Perna.

[2] William Echard adds "'Heart Full of Soul,' released in June 1965, is often said to have marked the arrival of raga rock [and] be pivotal in shaping the look and sound of 1960s psychedelia.

[8] He added that the vocal parts by lead singer Keith Relf, backed by atmospheric harmonies, provide contrasting melancholic and upbeat sections.

[4] McCarty and session bassist Ron Prentice (who also played bass on "For Your Love") comprise the rhythm section.

[5] Yardbirds' bassist Paul Samwell-Smith, who assumed the role of producer for "For Your Love", is listed as "Musical Director" on the Columbia 45 rpm single.

[15] During the group's second American tour, they played "Heart Full of Soul" (and "I'm a Man") for Shivaree, a pop music variety television series.

[19] Critic Ned Raggett calls it "an attractive remake of the Yardbirds' 'Heart Full of Soul,' making it sound very much like an Isaak original instead of a worshipful carbon copy.

[20] AllMusic's Thom Jurek describes it as "pure psychedelic Yardbirds elegance with a bunch of space and dimension added to redeem the track for the 21st century.

[21] Stephen Holden, writing for The New York Times, notes, "Enhancing the tarnished '60s ambience is a soundtrack that juxtaposes rock classics like 'Heart Full of Soul' from the Yardbirds [with current music]".