You'd be able to chew some aspirin to prevent it. You'd be able to call 911 and get the ambulance on the way. You'd be more likely to survive.
Perhaps a large portion of the 600,000 people who die of heart disease every year - would not.
The good news is this: Apple, which is reportedly working on a "smart" wristwatch, is working on just such a technology.
According to Thomas Lee and David R. Baker at the San Francisco Chronicle, Apple hired a "renowned audio engineer" named Tomlinson Holman to develop software and hardware that would allow a watch on your wrist to listen to your blood flow and then alert you when "turbulence" indicated that you were about to have a heart attack.
Prior to joining Apple, Holman worked for Lucasfilm, where he led development of THX - a sound system for movie theaters.
The bad news about all this is that reporting on the capabilities of Apple gadgets before they launch is often way off. It's getting better when it comes to iterative improvements on products with existing supply chains, like the iPhone and iPad. But for gadgets in new categories it remains iffy.
For example, we've been hearing about a new Apple TV for years now. People had all kinds of whacky ideas about what the iPad would look like before it came. Same for the iPhone.
Still, the evidence is piling up that Apple thinks it can make the iWatch something people want by making it something of a body-monitoring health-improving wearable computer. Most notably, it's been consulting with the FDA, and hiring impressive medical device talent.