The claim that Jane Goodall died from cardiac arrest is true. Entertainment Weekly reports that "Jane Goodall's cause of death has been reportedly revealed over two weeks after she was found dead while on her speaking tour in California." While the Jane Goodall Institute initially stated that Goodall died of natural causes when on her speaking tour, the article also highlights that TMZ obtained her death certificate, confirming that she had died at 91 from cardiac arrest. However, the original claim is right in saying that TMZ has often been an unreliable source, so I looked into it further.
Vanity Fair notes, "Goodall died in her sleep as a result of cardiac arrest, also known as cardiopulmonary arrest, according to her death certificate." Jane Goodall also apparently suffered from epilepsy, but it didn't cause her death. Other sources like FOX News, PEOPLE, and Rolling Stone all confirmed that Goodall did indeed pass from cardiac arrest.