Brian Loncar was found Dec. 4 in the front seat of his vehicle, which was parked in front of his downtown Dallas law office.
The Dallas County medical examiner's office says the autopsy showed hypertension and hardening of the arteries were secondary factors in the 56-year-old lawyer's death.
Loncar's death came two days after the funeral for his 16-year-old daughter, who killed herself on Nov. 26. According to Grace Loncar's obituary, she had battled depression.
Brian Loncar was well-known in Texas for his television advertisements, in which he branded himself the "strong arm."
Loncar's firm was based in Dallas, but his firm handled cases across the state.