This paper characterizes the optimal advertising strategy of candidates in an election campaign, where groups of heterogeneous voters are targeted through media outlets. We discuss its effects on the implemented policy and connect it to polarization. It is well known that polarization has increased in the past decades. Additionally, we empirically establish that polarization displays electoral cycles. These cycles can emerge as candidates find it optimal to cater to different groups of voters and thus to adjust policies. Further, recent developments in campaign advertising, such as targeting voters more precisely, tend to increase polarization. Finally, we show that even greater spillovers of the campaign among voters can increase polarization.