Hi 3boys, I'm not a fountain of knowledge or anything... Just been through this a few times and so have done loads of research!!
A large nt is just one marker for chromosome issues, likewise heart issues BUT does not necessarily mean either. I'm having a complete mental block but there is something that can cause a large neck measurement that is totally harmless and just resolves. Some babies, with measurements much much bigger than yours are born with a bit of floppy skin at the back of the neck don't worry it goes away) without any issues at all!
As for cvs and amnio its just worth mentioning that there is a non invasive blood test now available in the uk... It's horrendously expensive £500 for blood test and £150 for detailed scan, but its accurate and carries no risk to the baby. It's called the Harmony test. Where in the UK are you?
Another option you have is to go for a more detailed scan where they can look for things like the nasal none and blood flow etc... By doing this you get a better idea of odds.
When do you get your blood results?