The Do Container is executed as many times as their Iterate count parameter indicates. This parameter is evaluated statically when execution of the Repeat loop begins, so any changes to this parameter inside the loop (e.g. if it uses a variable) does not have any effect on the number of iterations.
To avoid infinite loops, all loops automatically stop after a set amount of runs. You can change this value in the Test --> Test Results Properties Page. The default value is 100. In case a (possibly) infinite loop is encountered, its corresponding Test Result Node is marked with an error marker. When executing tests using the testexec client, this value can be set by the -itermax command - line option.