the IVS is squeazed up against the rv which is collapsed owing to too much probe pressure so let up on the pressure a bit to ensure you see the RVID cleanly to differentiate the VS from the RVPW. also on the pwd you are measuring papillar along with the wall. You can also change your mmode to make it bigger on the screen and make the b mode smaller and this will help follow the endocardial lines better. Also dont get too concerned over a minor discrepancy especially in cat hearts as you can measure 10 times and get 10 different measurments key issue is to measure endocardial lines that are consistent and continual throughout the tracing.