Maine Coon sudden death

My 5 yo Maine coon healthy as can be (so we thought) just died in my bedroom this morning. After this morning she was as playful and cute as ever. She ate and drank and wanted cuddles and then we’re just found her laying on floor. We took her to the vet even though we knew it was too late. They said Maine coons have heart issues but then told me blood was “pouring” from her mouth? She has a sister the same age who’s seems fine, wtf happened :(.