I have also had rats with hypertrophic cardiomyopathy which is a different heart problem where instead of the heart becoming enlarged, it grows in on itself, reducing the sizes of the inner chambers. In this case, the symptoms are generally labored breathing and, in advanced cases, blue extremities. In this case, Lasix can be helpful, too, but Cardoxin is dangerous. Instead, I've been trying enalapril with some success. I am thinking about getting a couple of mice for pets.
Life span is about two years.
There are handouts which have basic information on mice, available from clubs, or you can look it up at bookstores or libraries. In any case, it is recommended that you learn all you can about a prospective pet prior to bringing it home. I had two mice, one male and one female. They bred and came out with a male and female offspring. I then separated the two males from the two females because I didn't want any more babies.