Complex sentence: And it is possible that it was this, along with an undiagnosed heart condition, that led to his death although the results of the post mortem have never been made public, beyond the official cause of death.
Split into simpler sentences: And it is possible that it was this, along with an undiagnosed heart condition, that led to his death. Although the results of the post mortem have never been made public, beyond the official cause of death.