That diagnosis seems unlikely. Heart failure rarely causes sudden death. She went from performing vigorously on stage to dead within a few minutes. Heart failure tends to cause fatigue and water retention that gradually worsen over months or even years. Heart failure from obesity also generally takes many decades to develop. She died aged 32. What she did have was a long history of sudden unexplained collapses. This strongly suggests she had an electrical defect in her heart. Finally, daily life says this is an unlikely diagnosis. Today we see tens of millions of super-obese people. If fatty degeneration of the heart die to obesity happened even one time in a thousand, there would be thousands of young fat people dropping in their tracks every year. Do the math. Every major metropolitan area would see the freeways turn into a parking lot several times a year as a young fat person suddenly drops dead while driving. Yes, obesity kills, but almost never like a bolt of lightning from the blue. It's much slower and more horrible than that. Mama Cass died from a heart arrhythmia. If she didn't have a defective heart, she would have died in the 1990s, massively bloated from fluid retention, half blind from macular degeneration, bedridden, toes amputated from high blood sugar, etc.