Maintaining a normal heart rate (between 60 and 100 beats per min) and rhythm (beats regularly) is vital for human health. The significant reduction in heartbeat (less than 60 beats per min) is called bradycardia. It has enhanced mortality rate because of the lack of effective treatment. Treatment patterns are changing, since 1960s a pacemaker was used for the first time in a clinical setting and revolutionized the bradycardia therapy. In this chapter, readers will learn the history of modern pacemaker, mechanism, function, and its pros and cons. Readers will be surprised to discover how smart a modern pacemaker is. Till now, pacemaker is the definitive treatment for a drug refractory bradycardia and has saved tens of thousands of lives worldwide.