really sorry to hear that @nightmanagerfan, it's a tricky one to know what you are going to do if you do find out the baby has downs, there is such a variety within the diagnosis as well. I know of a little boy with downs syndrome at my daughters mainstream school and he is the happiest and loveliest child ever!
Also remember that although the risk is 1 in 5, that is still a 4 in 5 chance of not being. Also there are so many things they can do with heart defects now, particularly as they have spotted it very early on - they can have the heart specialists there as you give birth to give your baby the absolute best chance of a fantastic life.
Yes it's a tricky time to deal with, and yes you have the absolute right to mourn the easy pregnancy you hoped for, but then pick yourself back up and keep looking at the positives. It is not a typical journey, but that just makes your journey more unique and special to you :)
It is worth asking for advice/support from your minister/church, but ultimately, despite being in the christian faith, you will know how YOU feel, and how YOUR family can best deal with the situation you have been dealt. And if that means termination is the best option for you both then maybe that is the option that you want to consider. Similarly you might feel that you want to go ahead, which is absolutely fine too, but you will hear naysayers for each side of the argument. Be kind to yourself, and be gentle with your emotions x