Probably not. Pacemakers can prevent bradycardia (slow pulse) or even heart block (no pulse). Some pacemakers can perform anti-tachycardic pacing, which can terminate some upper-chamber tachycardias. For the most part, however, tachycardias can not be treated by a pacemaker - and implantable cardioverter-defibrillator is required.
Depends. If what you have is purely a pacemaker that makes sure your heart beats at a certain rate per minute but is not able to detect a potentially dangerous abnormal heart rhythm then it won't help. Now if the device you have is a combination pacemaker and aicd (cardioverter-defibrillator) then this device is in theory capable of recognizing a dangerous heart rhythm and shocking you out of it.