A massive heart attack can kill a person instantly or at least within a minute or two.
But most times a heart attack including a massive heart attack doesn't kill people instantly but instead the death usually occurs around 10 to 30 minutes after having the heart attack.
When you have a heart attack including a massive heart attack you need medical attention right away so if you think you're having a heart attack you need to call 911 immediately and get medical services on the way.
The faster you get medical services on the way the higher chance you have at surviving the heart attack including the massive heart attack.
A massive heart attack is usually more serious than a regular heart attack is so medical attention is even more important then.
When your heart is not pumping or is under attack your brain cannot get oxygen which then leads to brain cell damage and the longer it takes to get your heart pumping and get you breathing again the higher chance you have at suffering brain damage.