A: The HELOC is an open-ended mortgage. The Second Mortgage is a closed end mortgage. On the HELOC you only pay interest on the dollar amount you take as an advance. You can continue to use the available dollar amount on the line for 10 years. In other words, the HELOC can be repaid and then you can borrow the money again and again. With the Second Mortgage you take the full amount of the loan at closing and interest starts accruing on a daily basis, and repaid on a fixed monthly basis.