How to replace dynamic values

Hi,
how we can get the dynamic values and add variable value in between dynamic contect..
Ex: I am fetching data from database i.e Dear [Fname], Here is your Transaction Id [tracid]
Here [Fname] and [tracid] should be replace with the variable value like fname = john, tackid =12345
C# Code:
Fname= Request.Params["Fname"]; Fname= Fname.Replace("[Fname]", Fname);
oMsg.Subject = oRefEmail.ExeSubject; 
currently "oRefEmail.ExeSubject" contains Dear [Fname], Here is your Transaction Id [tracid] , how can we replace it like Dear john, Here is your Transaction Id 12345
Thanks 
Sree