Is normal have supraventricular extrasystols after aortic valve surgery? can be dangerous?

Yes, and No: It's extremely common and generally goes away as the heart heals. Remember, you've got stitches right in the heart muscle for goodness sakes - a little irritation is expected. Assuming they go away (and in most cases even if they don't) the extrasystoles don't impact your lifespan and don't pose a danger to your health, though i'll admit they can be a bit of a nuisance.