Nope.
It has two independent clauses.
A) complete sentence
B) fragmet
C) run-on
I say it is A
It has two independent clauses.
You're getting tired and need a break!
The statement "The heart catheterization indicated some abnormality of the heart muscle, this may have possibly been a blood clot" is a fragment.
A complete sentence must have a subject and a predicate, conveying a complete thought. In this case, "The heart catheterization indicated some abnormality of the heart muscle" is a complete sentence because it has a subject (heart catheterization) and a predicate (indicated some abnormality of the heart muscle). However, the part after the comma ("this may have possibly been a blood clot") does not have a subject and does not form a complete thought on its own.
To make it a complete sentence, we could rephrase it as "The heart catheterization indicated some abnormality of the heart muscle, which may have possibly been due to a blood clot."