I'm new to this forum but I wanted to tell about my dogs death and ask opinions as to the cause . He was a 7 year old male , a large dog about 120 lbs he has been healthy . He had not ate much in the days before his death , when walking in the park ( his favorite place to walk free ) Friday he seemed slow and when on the leash he walked slower than usual .I thought he was sick , he could get in the car ok .He did not get to go to the park Saturday , but sunday he was enthusiastic about going to the park and walked briskly around checking things out ,he had a bowel movement at the park , he was in good spirits . Monday he did not get to go to the park but acted like he wanted to go as I dressed . Monday night he got in bed with me as usual for a while , then he got on the floor by my bed and I could hear him breathing deeply , he has his own door and he had gone to the back yard , I missed him and called for him , he did not come , about 2am I went out and found him laying on his stomack he would not respond , I rolled him on his side and he made a couple of twitches as if in pain and he was gone . I have not given him any heart worm medicine since last winter , and intended to get him checked soon , could heart worms have killed him ? he only was off the heart worm medicine for 7 or 8 months . Could he have had a stroke ? he was lethargic Saturday but seemed to feel well sunday and Monday , he died at about 3 am on Tuesday .Cancer ? heart attack ? he is buried now I don't want to get a autopsy , it would not help now .