<connectionstrings>
<add connectionstring="Data Source=.\SQLEXPRESS;AttachDbFilename=E:\PatientDetails.mdf;Integrated Security=True;User Instance=True" name="Connection" />
<add connectionstring="Data Source=.\SQLEXPRESS;AttachDbFilename=D:\PatientDetails.mdf;Integrated Security=True;User Instance=True" name="Connection1" />
<add connectionstring="Data Source=.\SQLEXPRESS;AttachDbFilename=G:\PatientDetails.mdf;Integrated Security=True;User Instance=True" name="Connection2" />
</connectionstrings>
From the code you can access like
string=Convert.ToString(ConfigurationManager.ConnectionStrings[0]);
OR
string=Convert.ToString(ConfigurationManager.ConnectionStrings[1]);
OR
string=Convert.ToString(ConfigurationManager.ConnectionStrings[2]);