-it is your responsibility to take good care of the pets in your life. you have a financial and emotional committment to them. you are required to feed, water, shelter, keep safe from harm, and spend time with them...love them...let them be dogs, cats, puppies, kitties, birds, iguanas etc etc.
-it is also your responsibility as a human being to gently let them go when they are struggling to catch a breath because they are suffering from congestive heart failure and there is nothing more that the docs can do...
-it is your responsibility, your duty to let them go with dignity, painfree, and in your arms. this is what you sign up for when you decide to share your life with a pet(s).
-know when the time has come, listen to your pet, because they will always tell you.
and if you can't understand this, i advise you to go to your local veterinary center where they have an ICU and take one of those nurses to lunch and have a question/answer session... then you'll understand.