What is heimdall PIT file?
Heimdall is a open source tool, used to flash firmwares for Samsung devices. Heimdall works some kind of different from Odin.Heimdall flashes individual files where as Odin flashes a package files. PIT file in Heimdall is used to tell your device how to boot.

It is general format and are considered one of the original formats for Macintosh file for compression. (.PIT) are MAC OS files. To open file this on Windows OS use 'Smith Micro StuffIt Deluxe 2010'.