HELOC to purchase second investment

[Elizabeth O.]

I bought my first property with a conventional loan.  I no longer have a lump sum sitting around to put down 20% on a second investment property.  I am looking into a home equity line of credit.   I have read great things about it being a way to get an investment property with almost no out of pocket costs as the interest is tax deductible up to 100k.  

Most things that sound to good to be true usually are.  

Main concern is the obvious; leveraging my primary residence.  

I was able to accomplish cash-flow with my first investment. If I do my due diligence and make sure I can cover my mortgage and then the PandI on my HELOC what else do I need to be aware of?

Will this hurt my credit?

Is this truly a way to get ahead if you are cautious on your investment and don't just have big piles of cash lying around?

Thank you very much for reading this and I look forward to reading any and all responses.