Whenever you bring another bun into the household, if the current pair can see or smell it, there’s a chance it can break their bond. If she’s now attacking her mate, you need to really separate them and/or move the new bun to another room.

What’s CHF? I understand he may not live as long (you expect him to pass in a few years?) but that doesn’t mean he shouldn’t be bonded. Not saying you have to bond him with your pair if you don’t want too, but I wouldn’t not bond him because he may only live a few more years.

Ah okay. Bonding might not be wise then. I had no idea. I don’t think the pair should meet your single bun if they’re not going to be bonded. I suppose you could pre bond tho just to get everyone accustomed to each other’s scent so maybe sharing the playroom won’t be as big a problem for your female.

Keep an eye on your pair – I had to split my pair up when I brought a third bunny home as my female just got too aggressive and was bullying her partner. However, we’re now 4 months down the line and I’m almost ready to call them a trio.

I agree with Sarah – try some prebonding, swapping them between spaces and litter trays so they at least get used to the scent of each other. Hopefully your females aggression will calm down. You might find over time that they start lying together through bars etc, which could be a sign that they are open to bonding. Since he has the heart condition maybe it’s not worth going through stressful bonding, but rabbits living nearby may naturally come accustomed to each other, and you may well have an easy bond in a few months time if you wanted it.