In the 1950s, many old series B-westerns were chopped down to a length that would allow them to be placed in a one-hour time slot. Because of this, it's common to find multiple versions of Roy Rogers, Gene Autry and Hopalong Cassidy films. The version of "Heart of Arizona" I saw on YouTube is the recently restored one that returns the picture to its original 68 minute run time.
The story does what MANY series westerns did back in the day...it uses the name of a real life western figure but completely fictionalizes them. In this case, early in the story, a deputy is manhandling Belle Starr following her release from prison. Hoppy witnesses this and like you'd expect, he stands up for her...decking the deputy and freeing her.
Later, after Belle arrives at her ranch, she realizes she has a problem...someone has been stealing her cattle. But how will she and Hoppy find out who's behind all this wickedness?
"Heart of Arizona" is enjoyable but not especially well written. Not only does it fictionalize Starr, but there are some serious logical problems with the script. In one case, a 9 or 10 year-old boy is given a gun and told to guard a prisoner....and this happens two different times!! The worst, however, was near the end when the sheriff is about to make an arrest on the gang who is rustling. He approaches this group of criminals alone...no backup whatsoever!! Take a WILD guess what happens next?!?! The writers just were a bit lazy in this one.