Already explained before how meaningless a character coughing up blood is. Luffy's punch to Garp drew more blood than Squard's stab to WB. Law said Counter Shock didn't work on Vergo despite it covering his face in blood, which inconsistently changed in splatter size throughout panels on the same page, and Doflamingo coughed up blood from a superfluous attacks that had no effect on him in the long run. The only significant times WB coughed up blood was when he was having a heart attack, which is only significant because they were during heart attacks.
The sword never pierced his chest.
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And of course he held the wound, it's a giant gaping hole in his stomach, it will cause pain. The notion that it caused his heart attack, however, was dismissed by Oda having two characters, one with in-depth knowledge on WB's condition and worsening health, attributed something else to the heart attack and by Oda having WB laugh off the notion that the stab was serious.
Covered above. If the heart attack played a serious role in WB's health, Oda would have gave some indication to it. Yeah, it's common sense to assume that the stab played a role. I don't think the assumption is valid because Oda had WB dismiss it and the heart attacks were attributed to his age. Even if the stab played a role in the timing of the heart attack, as LBeezy said, Akainu would still be able to outlast WB, especially when WB's health was low enough that his reactions dropped to allowing Squard to strike WB without some attack from before.
If WB's health, with no other stabs or damage, ailed enough to let someone as weak as Squard to get a blow in one Whitebeard, one that you think could trigger his heart attack, then why would the same not happen for Akainu during an extended fight? And if the sword could trigger a heart attack, why wouldn't Akainu's attack do even worse? Either way, it still stands that Akainu would be able to outlast Whitebeard, and if
So you think Luffy's punch to Garp caused more damage than Red Hawk did to Doflamingo?
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Zero effect? Nope. Did it cause the heart attack? Manga suggests the opposite.