In open-list PR systems, citizens vote for the party and also for a particular candidate on the party ballot. In the Czech Republic’s flexible-list variation of the open-list PR electoral system, voters first select the party list to support, and then they have the option, but not obligation, to express up to four candidate preferences. Are certain voters more likely to cast preference votes? And when voters do cast preference votes, to what extent do they rely on heuristics, such as candidate ballot position, in making their candidate selections? In the present study, we use the October 2017 Czech National Election Study to analyze preference voting at the level of individual voters, which allows us to study the impact of political sophistication on voters’ behavior. We find that politically sophisticated citizens are more likely to cast a preference vote and to cast the maximum of four. Our findings with respect to ballot position effects refute the expected negative relationship between sophistication and voting for the first candidate on the ballot. Instead, voters who exhibit higher levels of political knowledge tend to vote substantively more often for the list leaders.