If you want to add personalisation to your subject lines we have the following fields that it's possible to use:
 
Contact last name - #contact_lastname#
Contact first name - #contact_firstname#
Attendee last name - #attendee_lastname#
Attendee first name - #attendee_firstname#
Event name - #event_name#
Event date - #event_date#
Event date and time - #event_date_and_time#
Venue name - #venue_name#
Venue town - #venue_town#
 
In the email subject line, add the above syntax.
e.g. #contact_firstname#, you're invited to #event_name#