Denise,

I'm glad that you asked the question because I have the same concern as you do. I have a 12 yrs old American Eskimo who is diagnosed with Chronic Renal failure in his kidney. I don't want him to "live" for me or anyone. I wish we know always know the right answer.

I have seen your earlier post...it is a very hard decision...I tend to lean towards sooner than later...when a dog is this old, and in this bad of shape, hips, heartworms (heavy) and cancer, he, cannot be really comfortable. But this is not my pet. This is a dog I saved, and knew, this would come...I wanted him to have the dignaty, he deserved and not be burnt up in a city facility. I wanted him to know that someone, thought he was special enough, to love, even if just for a few days. I do not want him to suffer any longer than he has to....I believe the kindest thing to do, is ease the suffering....it is just a matter of when.........

I don't post often but will reply because I went through a similar situation with my dog.
My standard poodle went through a bad bout of prostatitis when he was around 11. At almost 12 it returned again and this time I took him to Guelph University (ON) for biopsy, and full body x-rays. They diagnosed him with transitional cell carcinoma of the prostate, early stage yes, but still cancer. He was put on Metacam, Baytril, etc. The infection cleared up and based on a study he remained on Metacam because it had been found to somewhat slow the progression of the disease. He lived until 13 1/2, beyond the average life expectancy for a dog with this disease. I credit that to his excellent health. Only the last 3 months or so, was he starting to be uncomfortable so I changed his diet and that helped for a while. It was not easy, because as the prostate enlarged he had a lot of trouble urinating and would dribble. The last 3 weeks I was manually helping him relieve his bladder.
It must be noted however, he was not a large dog (42lbs) and the x-rays done when he was 12 showed absolutely no signs of arthritis, either in his lumbar spine region or his hips. The specialists said if it wasn't for the cancer he could easily live quite a few more years. He definately did not look or act his age.
This dog sounds like he has a tremendous amount of health problems, he is older than my Max was, and he is a big dog. You could try and clear up the infection and see if something like Metacam would help, but you still have the heartworm. It is very hard to let go when they come to the end of the line, but maybe it's his time.

Dr. Alice Villalobos has a "Quality of Life Scale" that helps owners with this decision. Dr. V is an oncologist, but she also has a special place in her heart for all geriatric pets.:

http://www.veterinarypracticenews.com/images/pdfs/Quality_of_Life.pdf

We had to put our last shepherd down at 5 years old. It was the hardest decision I ever had to make! She was such a sweet, loving, wonderful dog. She had hip dysplasia, but what finally got her was hemangiosarcoma, a rapidly progressing bleeding tumor. We had the luck of having a great specialist who diagnosed her. He was so good with her and caring, and told it like it was: no cure, will advance quickly and possibly cause bleeding out. He had told us when the dog loses interest in food, that's when you really know. We got the diagnosis on Friday, and by Monday she was dragging herself, bleeding from her behind, and wouldn't eat steak. We called this wonderful specialist and he told us it was time. We knew it too, without a doubt.

It was a terribly heart wrenching day for us, but she was so peaceful. She lay in our arms while they gave her the meds, content and happy to be with the ones she loved most. I'm tearing up thinking about her!

You're a special person to take this dog into your life.

Thanks Susan for that link.
Actually Max had a great appetite up until his last night. He always showed an interest in food, his surroundings, etc. He was on good pain management. His bladder got to the point that it was so stretched from being overfull that it ruptured when I was expressing it. I was actually bringing him to the vet that week to be PTS. Instead I was rushing him to the emergency clinic at 2am for surgery. I just had to know what was going on. I stepped into the surgery room with the vet while Max was under and opened up and we discussed his options (which I really knew were none). I was shown his ruptured bladded and it was even very difficult for them to catheterize him before the surgery. He was PTS on the operating table without ever waking up and I was with him. It took me months to get over the guilt. This is the first time I had ever gone through it.
I could have probably taken him in the week before, but honestly he was eating, still loved his car rides, his trips to Tim Hortons, a bit of fetch, etc. It was very hard to come up to that decision.
Having gone through debilitating progressive diseases with my grandmother and mother, it was very hard to go through the end with my dog who was on my mother's hospital bed when she died.
Max will always have a special place in my heart as my first canine love.

Also I found another link that might help to see if dogs are in pain. http://trends.aahanet.org/eweb/images/Trends/PDFs/DogHandout.pdf

I'm not worried about the heartworms...dogs live years and years with them without too much fuss in their daily lives. What would concern me is whether they can eat/drink/walk/play without any serious impediments. Blood in the stool could be many things, many of which aren't fatal if treated, obviously.

I do not envy you...I went thru a recent event that has really hurt me with my dog. It wasn't as bad as losing my kids, but almost. I started to volunteer at a local pet adoption place here locally, but I can't deal with the separation aftermath right now.

God grant you the wisdom of Solomon

It is always a hard decision. I had a GSD pup once. I loved that dog to bits and she went everywhere with me. She was perhaps only 4 months old when she started iching an scraching. She was skinny because of her poor appetite. Vets couldn´t find anything wrong with her. She scrached and scrached off her hair. We tried different foods to rule out food allergies, changed the carpets to rule out allergy to those and I lived in the woods in a tent for a week to rule out allergy to anything else in out home but nothing. People in the streets yelled at me for torturing a dog because she was really thin and had hairless thick skin on her sides. But she had that spak in her eyes! She whould go to the stable with me every day. Accompany us to the pasture and on horseback hikes. She was a happy dog. But at some point it started to fade... I had to wash the floors from blood when I came from school because she had scrached herself so much... She was in a pretty bad shape but we whould still go out for walks and morning jogs and love eachother. I remember one evening when she was down on the carpet in front of the door and looked up at me and I knew- the spark was gone. She was happy no more. My mom didn´t want to do this right before the christmas so she was with us for her first, last and only christmas. She was put down a day before she whould have become one year old... I was 16 and that tore me apart. But now I know that I will know when it is time and even though it still hurts like hell, I know that it was right. It is never easy but there are times when it is right.

I think you need a diagnosis on the bleeding, and should not assume prostate cancer. If it is advanced PCa he will be in a lot of pain, but I imagine it could be a bad bladder infection, or another cause. If he acts interested in life and in food, and can manuver on his own, I would keep him alive and comfortable. If he is in pain, or stops eating, I would let him go before it gets worse. This is all a very personal decision, good luck to you, and thanks for giving him at least a brief respite from the shelter.