Sudden death of cat...what happened??

We lost our 7 year old cat last night. He was a very healthy cat and seemed fine all day, even chasing the dog that morning. He had taken a nap later that evening and about 8:00pm, we heard him make this awful meow, but thought he was having a dream. He made another sound and next thing we know he stops breathing. My husband tried to resuscitate him, but nothing. He was gone. There was no blood, we have no poisons for him to get into, it was just so sudden. We can't figure out why this happened to a healthy cat. Is there a reason how a cat could die so sudden and fast?

I am so sorry for your loss and you have my deepest sympathy.
   
There is a particular heart problem that affects young to middle age cats. The cat appears perfectly normal and then just dies. My friend lost her cat this way two weeks ago. They raced him to the vet as they saw it happen but he could not be resucitated. The vet told them about the heart condition.
   
It sound like this is what happened to your guy.