"Heart of Glass" is one of those songs that managed to change the playing field for an entire musical genre. By virtue of the song's unqualified success, reaching number one in both the U.S. and the U.K. and beyond, the stakes for the new wave/punk movement had been raised. Before "Heart of Glass," the music's full commercial potential had previously been limited to cult status in line with the small underground scene from which Blondie had emerged. Now it was being realized. What began as a flagrant attempt to exploit the then still raging disco scene turned into the perfect genre-blending dance-pop gem. In fact, an early demo recording of the song was entitled "Once I Had a Love (aka The Disco Song)" and was included in the 2001 reissue of Blondie's Parallel Lines album. The earlier recording is telling, illustrating producer Mike Chapman's diligent work ethic transforming a loose, middling dance-like number into a taught, driving piece of gleaming dance-rock. As Chapman himself explains in the reissue liner notes, "At the first rehearsal we worked on "Heart of Glass." This proved to be a blessing and a huge step forward in cementing our working relationship. It was a great idea that needed to be put into the right shape to find a home on American radio play lists. Since both Debbie and Chris were intrigued by the current disco avalanche that was sweeping the country, we decided to go there with the arrangement." Even in its earlier incarnations Chapman and the band seemed to sense that the song was a career-changing opportunity and threw themselves into its recording as never before and the result paid off. The band wastes no time setting the rock-solid groove, crashing in behind a percolating drum machine with a throbbing bass line and steady four-on-the-floor bass drum supported by pulsing keyboards and plunky guitar lines. Singer Deborah Harry's vocal takes a more demure tact from the album's more brassy pop/rock numbers, opting instead for a high-pitched cooing, her voice softened by silky double tracking as she muses on the fragile nature of love, "Once I had a love and it was a gas/Soon turned out had a heart of glass/Seemed like the real thing, only to find much o'mistrust/Love's gone behind." Her voice drops slightly for the equally catchy chorus, supported by harmonized male backing vocals as she confesses, "In between what I find is pleasing and I'm feeling fine/Love is so confusing, there's no peace of mind/If I fear I'm losing you/It's no good, you teasing like you do." An organ swells in behind to take over the infectious melody with lush backing "la, la, la"s adding yet another layer of polish. The arrangement has a long vamp out, Harry's vocal dropping out for several minutes, letting the band run with the groove, perhaps with the idea of mimicking the length of many disco hits of the day with the backing vocals and organ carrying the melody as the track clocks in at nearly a full six minutes.