Fetching Cursor Is Very Slow

The problem I'm facing is when fetching a cursor is very slow. For e.g. below, when I debug the procedure until line 15 (FETCH test_cur INTO ...), it's stuck for a while about 4 or 5 min, but if I run through, it's stuck though I leave the executing 2 or 3 hours...

Does anyone know why when the excuting reaches statement FETCH test_cur INTO ... (line 15), it stuck there? I'm using Oracle 11g.

1       ...

2       PROCEDURE xxx

3       (...)

4       IS

5       CURSOR test_cur IS

6        SELECT ...

7

8       BEGIN

9        ...

10      IF NOT test_cur%ISOPEN THEN

11          OPEN test_cur;

12      END IF;

13

14      LOOP

15         FETCH test_cur INTO ...

16

17         EXIT WHEN test_cur%NOTFOUND;