3 year old male cat died after surgery, why?

Hi,  I recently brought my 3 year old male cat to the vet because he was showing symptoms of a urinary blockage like one of my other cats had before.  When I brought him in the vet confirmed that yes he did have crystals blocking him from urinating. They rushed him to surgery and she called me 2 hours later and said that he passed away. When they went to turn off the anesthetic his heart stopped, they tried cpr but it just didn't work. My question lies on the fact that my other male cat had this surgery twice and it was successful both times. Why wouldn't my 3 year old male cat not make it through? Any help you could give would be appreciated as I've been a complete wreck since I found out. Thank you..

[nancyjac]

That emergency surgery was performed indicates that his condition was already life threatening before the surgery.  If this cat sustained internal organ damage from toxicity build up during the time leading up to the complete blockage, he would be at a higher risk for the rigors of any surgery.  It is also possible that he had an unrelated heart condition, or that he had an anaphelactic reaction to the anesthesia.