It's been 40 years since Blondie's "Heart of Glass" topped the Billboard Hot 100 chart.
The band had written an earlier version of the song called "Once I Had a Love," but they weren't happy with the reggae feel of the arrangement. They also tried it as a ballad, but that didn't work, either.
Then, at the height of the disco craze, they decided to turn it into a disco dance song. The song's name was changed to "Heart of Glass," and it went No. 1 on the chart.