According to Wright, the play's typescript "was heavily revised in Shaw's handwriting, in different shades of ink, often with pasted over sections." The original title for the piece had been The Studio in the Clouds, which doesn't have quite the ring of Heartbreak House. Most shocking to me was the fact that Ellie's spiritual marriage to Shotover seems to have been an afterthought, inserted on a page of handwritten dialogue added to Act III.
Other additions reflected current events. The First World War was progressing as Shaw wrote the play. After combatants introduced tanks at the Battle of the Somme in 1916, Shaw added references to tanks in the script.
The play's ending, with a bomb falling from a passing Zeppelin, also seems to come from an incident in 1916. On the first of October of that year, a Zeppelin passed over Shaw's house and was shot down only a few miles away. Shaw wrote in a letter:
The sound of the Zepp's engines was so fine, and its voyage through the stars so enchanting, that I positively caught myself hoping next night that there would be another raid. I grieve to add that after seeing the Zepp fall like a burning newspaper, with its human contents roasting for some minutes (it was frightfully slow) I went to bed and was comfortably asleep in ten minutes. One is so pleased at having seen the show that the destruction of a dozen people or so in hideous terror and torment does not count.
Shaw's own sentiment echoes the final lines of the play:
MRS. HUSHABYE. But what a glorious experience! I hope they'll come again tomorrow night.
ELLE. [radiant at the prospect] Oh, I hope so.
Wright notes that when the play was revived in the midst of World War II, with bombs again falling over England, Shaw added a line by Shotover: "Well said, child. They will awaken your country's sleeping soul." It was probably right for the moment, but the ending is more powerful without Shotover's coda.