A massive heart attack and a regular heart attack are similar but the difference between a regular heart attack and a massive heart attack is that a massive heart attack is worse than a regular heart attack because a massive heart attack causes damage to more organs and effects more organs than a regular heart attack.
When you have a massive heart attack you're more likely to die than when you have a regular heart attack.
You can still sometimes survive a massive heart attack though if you get medical attention right away but if you can't get medical attention then you'll likely die soon after having the massive heart attack.
In medical terms a massive heart attack is considered worse and is a myocardial infarction that destroys a large amount of tissue.