Will applying for HELOC screw up a loan I already applied for?

[Tom Heneghan]

I've been looking for an investment property but was unsure of what type I wanted. I have enough savings to put a down payment on a conventional loan for a house and got a pre-approval letter. After that decided I might be able get a duplex - four plex if I used HELOC to increase down payment.

I put in an app for a HELOC with my local bank. They have given me a preliminary approval and are going to set me up with an appraiser.

In the mean time I found a house that like and put in an offer. My question is this. Is there any way that getting a HELOC might screw up the approval of my conventinal loan? Will the home lenders see the application for the HELOC and change their minds? Would it be better to let the loan go through and then apply for HELOC?