Joanie was picked up by her former friend Lisa Dingle (Jane Cox), the woman whose husband she stole and married.
On the drive back, Lisa explained to Joanie that she was now back with Zak (Steve Halliwell) and he wanted a divorce.
Shocked by the news, Joanie fell back and died without any warning.
Lisa later explained to Zak that she had called an ambulance but it was too late.
Joanie Dingle suffered a cardiac arrest and died on Emmerdale tonight
Joanie was being driven home from prison by Lisa Dingle when she had the heart attack
Those watching at home were taken aback by the death, which occurred before the first advertisement break.
One social media user commented: “Well that scene of Joanie dying was a bit errrr, quick.”
“Wow, they just killed Joanie off like that,” another remarked.
Lisa had to break the news to Zak later on
Emmerdale's most shocking moments
Thu, January 5, 2017
Emmerdale's most shocking moments: Explosions, car crashes and murder – life in the Dales is never dull. Here are the most dramatic scenes from the popular soap.
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Emmerdale's most dramatic moments
Someone else said: “That's an awkward plot device. Kill Joanie off because you don't need a divorce or custody battle now. #emmerdale.”
While a fourth asked: “That wasn't a BIG shock/twist? I expected it. Joanie….Really? @emmerdale #emmerdale.”
Last year, fans of the soap were left reeling after Holly Barton (Sophie Powles) died suddenly from a drug overdose.
Emmerdale continues tomorrow at 7pm on ITV.