My sweet Jaques

My baby kitty Jaques Pepin, passed away yesterday afternoon. He was just shy of 9mos old. I had him neutered this past Friday and when I brought him home, he seemed fine. However, he had a heart defect that the surgery kind of brought to the surface Wednesday afternoon. I went home early due to the weather and when I saw him, I knew something was wrong. He was panting heavily and could not move on his own. When I brought him into the vet, she gave him a diretic and tried to get him to release some of the fluid buildup but it did not work. Late yesterday afternoon, he died. I miss him so much it hurts physically. I held him for a long time and I still feel like there should have been something I could have done.