I have two dogs, one is a male golden retriever, and the other is a female golden mix (both are fixed). They've been in the same household for three years. The female is generally a lot more aggressive than the male (who is usually so clam he's basically a piece of furniture), but previously they've never gone further than play fighting. Today they have been fighting for real. I am sure they would have fought to the death without intervention. The first time I'm pretty sure the female started it, she jumped on him and starting to growl/bite. She was put outside, and he stayed indoors. After a half hour, I let her in. The male went up to her and started biting her first. This time it was VERY difficult to break them up. I put them in their pens, and after after two hours they seemed calm, so I let them out. This time, she went berserk first and really went after him. I managed to drag them into separate pens and I'm not letting them out at the same time again. She has a bloody ear, but he doesn't have any visible injuries. I called the vet, and he had no advice besides "keep them separated". They weren't fighting over food or another animal. They are not aggressive towards me. This has never happened before, and I don't know why something changed so suddenly after three years. Tomorrow I am going to have them checked out (separately!) by the vet to make sure one/both of them are not ill. I can't keep them separated forever... I love them, they are my dogs. Sticking two large dogs in different rooms indefinitely is not practical, nor is it practical for me to keep putting myself in between two snarling, biting, and fighting dogs. Their added weight is nearly 200 pounds, so it's dangerous for both them and me. I love them both, and if I had to choose between one to keep and one to give away would break my heart. I'm actually tearing up just thinking about it. Has anyone seen this behavior before? What could have gone wrong with my dogs?