Rat Lethargy

Question
My rat Langston is around 6-8 weeks old. When we got him this past weekend he was extremely active and friendly. For about a day now he has been very lethargic. I've read this could be a sign of cardiac problems(in older rats) or respiratory problems. He doesn't have any discharges from the eyes, mouth, or nose. His respiration rate is very high, and he seems exhausted when we try to play with him. Do you have any idea what may be wrong?

Answer
Even a baby rat can have heard problems if he were born with a congenital defect.  

I would take him to the vet. Often, fast respirations can mean respiratory infection even if they are not sneezing or have sounds of congestion.  Do you have a vet for him yet?

If not, let me know and I can help find one.