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?
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.
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.