I’ve never had one but have known people who’ve had. They seem to be in alot of pain. But why? Basically, the heart just stops beating. I can’t see where the pain comed from.
That should be heart ATTACKS. I’m falling asleep at work while posting this.
Pain is the body’s natural defense system for telling you that Something Very Bad Is Happening. Since the heart is probably the most vital organ in the body, it makes sense that any threat to the heart’s viability would hurt. A LOT.
Not all heart attacks are fatal, but imagine if you kept on shooting hoops while your heart starved for oxygen? You’d finish yourself off right quick.
For some reason, the brain is the only organ with no pain nerve endings whatsoever. Which proves that, for most people, the brain isn’t a vital organ after all. 
I’d imagine it has to do with two things. I am not a doctor, so this is mostly speculation based on other knowledge of muscle pain. Muscles hurt when they have a lack of oxygen…when the heart stops, the blood stops flowing, and it can’t get oxygen.
Reason #2, and probably the more contributing factor: A heart attack could be considered a cramp of the most powerful muscle in the body. Ever had your hamstring cramp? Know how painful it is? Well, it’s like that but with your heart.
Again, these are mostly WAGs, which I usually wouldn’t put into GQ, but I think they are well founded WAGs.
Jman
IANAD - but I can speak from personal experience.
In a heart attack (myocardial infarction) the heart does not necessarily stop beating. The problem occurs when an artery in the heart is blocked (usually by a clot formed when plaque in the artery ruptures). The muscle tissue in the region served by that artery stops receiving fresh blood - that means no oxygen, and also that all the waste products of the muscle cells start to accumulate. In other words, the part of the heart served by that artery starts to die.
That hurts, and it hurts a lot more than cramp.
The extent of the patient’s recovery after the attack depends mainly on how much of the muscle and nerve tissue in the heart was destroyed. I was lucky.
In some cases the blockage is not complete, or the artery is blocked well “down the line” so the patient can survive some considerable time before needing treatment. Indeed, there are “silent” heart attacks when the patient is unaware of what just happened and carries on a normal life after the attack and the damage to the heart muscle is only discovered at a later date.
You are confusing heart attack with cardiac arrest. A heart attack means that blood flow is obstructed to some part of the heart. Cardiac arrest means that the heart stops beating. A heart attack may cause enough damage that cardiac arrest occurs but the two are not synonymous. As johncole said the pain of a heart attack is because heart muscle is dying from lack of bloodflow.