Yes. Tickets are reserved for you for up to 10 minutes when placed in cart. Once tickets are added to your cart, you'll see a timer in the upper right-hand corner of your screen. The timing varies per event and will be displayed to you on the event page while checking out.
If that timer reaches 0:00 before you have completed your order, the tickets in your cart will be released. Once released, tickets will be returned to the available pool of inventory and may be selected by anyone else.
Once the cart timer expires, you will be prompted to search for new tickets.