Second-degree heart block may result in the heart skipping a beat or beats. This type of heart block also can make you feel dizzy or faint. Third-degree heart block limits the heart's ability to pump blood to the rest of the body. This type of heart block may cause fatigue (tiredness), dizziness, and fainting. Third-degree heart block requires prompt treatment because it can be fatal. A medical device called a pacemaker is used to treat third-degree heart block and some cases of second-degree heart block.