You always manage to make me really think about even the smallest of things in scripture. *BIG SMILES*. I have linked your post re this subject, below I have always taken these words to mean that their hearts were faltering. Not actually stopping and causing death.
When I am fearful or my heart has been "broken" by betrayal - it really does affect my heart. My heart races when I am frightened and aches with pain when I have been hurt by someone I love. I am sure we are all the same. But, your questions did make me really think just how terrifying the end times will be. Almost unbearable fear.