In the article linked here: https://help.heartbeat.chat/en/articles/6720335-what-are-event-email-notifications), it states:

"When you update the time or location, invitees are automatically notified. For all other updates (such as name changes, description, etc.), you're given the option to notify invitees or not."

However, I noticed that I not always have that option, and updates are sent out when I modify titles and descriptions.