If the dogs anxiety gets severe enough then the dog may have a heart attack or die from the severe anxiety.
Or if the dog already has heart disease or is at risk of a heart attack already then the severe anxiety may suddenly cause a heart attack.
But most cases of anxiety for the dog are not severe enough to cause a heart attack or death.
But still it's a good idea to help comfort the dog when they have anxiety to prevent any possible health issues with the dog.
Too much anxiety in the dog may also increase the risk of the dog having a heart attack or cause the dog to develop other heart issues.
So do your best to keep the dogs anxiety down.