Well, it's causing muscle contractions. At high enough intensity, it should raise your heart rate. It's just a matter of what intensity level is tolerable during sleep (and the effect on sleep quality), no?

No, that would wake you up long before it had cardiovascular benefit. You need your heart rate up into zone 2 to 5 to really have a positive impact. That's 120 BPM plus for most people. Once you're around 80 it'll wake up anyone, even someone with very low cardiovascular fitness.

I read with the right dream (nightmare) heart rate can climb to 180.

If you slowly condition yourself I think you can exchange sleep quality for increased heart rate.

But I suspect the heart needs rest too and you will die.

An isometric hold would be better I think. You don't get any vo2max improvement but it does improve cardiovascular health.

That's an interesting idea. Do you know if anyone's tried it?

> Once you're around 80 it'll wake up anyone

Source? I haven't been able to find info on this. I get resuls on nocturnal tachycardia and such. Nothing on elevating a sleeping person's heart rate and observing the result, though.

To be clear, if you implanted a lead, you might not wake them up. It's the mechanism by which you would raise their heartrate that would wake them - the same things that elevate heartrate from external stimulation would also cause cortical arousal.