Randy Savage died due to a heart attack from arrhythmia per brother

According to "Macho Man" Randy Savage's brother Lanny Poffo in an interview with Bright House Sports Network (article here, video excerpt here), Savage's death on May 20th was due to a heart attack from ventricular fibrillation (VF or vfib for short), a type of severe arrythmia (abnormal heart rhythm).  More of the interview will be aired on Toyota Sports Connection tomorrow night.  There was no mention of whether or not this was the official word on the cause of death in the article or interview excerpt posted by BHSN.

With his brother quickly losing consciousness, Poffo said that "What it means to me is, it was a beautiful way to die. It's quick, painless."  He also called Randy's wife Lynn a hero for immediately grabbing the wheel to try to get them out of traffic.  "Randy's foot was still on the accelerator. She reached over and steered the Jeep Wrangler into a tree, saving the life of a motorcyclist and possibly a bus. You know, there's no telling what can happen when you're going the wrong way."

The comment section of the article has been flooded by people pointing out that vfib is the immediate cause of death, not a long-term condition.  It's the result of something else that then will lead to death if not the heart is not shocked with an external defibrillator.  As PubMed puts it, "Ventricular fibrillation is a medical emergency and must be treated immediately to save a person's life."  Presumably, the contributing causes will be revealed in the autopsy report.  The initial autopsy was ruled inconclusive pending the results of toxicology and histology (small tissue sample analysis) reports.

The elephant in the room has been anabolic steroid and possibly human growth hormone (HGH) abuse, as Savage was a pretty small guy who got bigger and bigger over the years (with the exception of his last few years in the WWF when they were seriously testing and he started wrestling in a shirt) before suddenly shrinking several years ago.  He changed so much to the point that he refused to take his jacket off during his brief TNA run, and the local rumor was that his doctor told him to get off steroids immediately.

At the very least, it's sort of a foregone conclusion that the medical examiner found an enlarged heart.  A enlarged heart (often with left ventricular hypertrophy, thickening of the muscle in the lower-left chamber of the heart) has been a common finding in wrestlers who used steroids and/or HGH, with left ventricular hypertrophy often being a contributing cause of death.  Among many others, Davey Boy Smith, Eddy Guerrero, Chris Benoit, and Curt Hennig all had enlarged hearts, and all were like Savage, smaller wrestlers who gained ridiculous amounts of muscle mass thanks to chemicals.  Of the four, only Benoit died of unrelated issues (suicide after murdering his wife and son).

Hennig died of cocaine poisoning, not an overdose, which is often incorrectly cited as his cause of death.  With Hennig, the cocaine itself was in a non-lethal dose but his heart was too damaged to deal with it.  Smith and Guerrero suffered heart attacks and in both cases, the medical examiner ruled that steroids were a contributing cause.  Guerrero's widow, current WWE performer Vickie Guerrero, later had the death certificate sealed.  Meanwhile, Smith's father was in denial that his son (who also had severe issues with painkillers and cocaine) had ever touched drugs and believed that Davey was murdered.

Smith's cousin and long time tag team partner, Dynamite Kid, who introduced him to steroids and had an even more dramatic transformation himself, wrote in his autobiography "Pure Dynamite" that he quit steroids after doctors discovered scars on his heart from enlargement.  It's also been alleged for several years that a current major star of a similar profile to the others mentioned here told friends that his doctor diagnosed him with an enlarged heart.

That's not even touching on naturally larger framed wrestlers like John Kronus who had enlarged hearts from steroid abuse...