My condolences to you...
A few years ago, I lost my beloved Doberman Pinscher to a random terminal heart failure...the vet said it was a genetic flaw in the Doberman bloodline...there is no cure, no means of predicting it, and no means of vaccination.
I hope it goes painlessly...it's all you can hope for at this point.
"As you do not know what is the way of the wind, or how the bones grow in the womb of her who is with child, so you do not know the works of God who makes all things."
-- Ecclesiastes 11:5