In C++, is there a difference between “throw” and “throw ex”?

I'd like to ask this question (also here), but this time about C++.

What is the difference in C++ between

try { /*some code here*/}
catch(MyException& ex)
{ throw ex;} //not just throw

and

try {  /*some code here*/}
catch(MyException& ex)
{ throw;} //not throw ex

Is it just in the stack trace (which in C++ is in any case not a standard as in C# or Java)?

(If it makes any difference, I use MSVS 2008.)