Cursor gets slower and slower

Hi We have a cursor with about 600'000 records. And it seems, that the cursor moves slower and slower through the records. At the beginning, it is very fast. At about 10% (at record #60'000) it is 10 to 20 times slower! Is it true, the more records are in a cursor the slower is the progress of the records later in the cursor? Thanx for any answers Chris