How long will a pacemaker last?

10 years. Depends on the model of the pacemaker and when it was put in. It's not uncommon for pacemakers today to last 10 years or longer. Part of that is dependent on how many times its had to kick in.
Pacemaker. Pacemakers function lasts depending on battery depletion and decay. The more drain on the battery the shorter the battery life. The average pacers last 4 years if discharging constantly, 7 years if not on constant drain and up to 12 years on minimal drain. The newer battery technologies should last longer in theory.