Presently, smartwatches are becoming increasingly popular; however, their small screen size poses challenges to visualization research, particularly specific data, for instance, fitness, sleep, and heart rate, visualizations. Previous studies represented real-time heart rates (RT-HRs) using heart rate values or heart rate values with an icon, and have made a preliminary exploration of heart rate data visualization on a smartwatch. However, which type of heart rate data users need most, how to visualize different types of heart rate data in smartwatch small screens, and how to allow users to quickly glance at their desired information have not been studied. In this study, we explore users’ preferred heart rate data type and preferred visualization on a smartwatch. We found that the participants’ preference scores for average heart rate and exercise intensity are higher than the scores of RT-HR and heart rate records, implying that most participants prefer interpretative data instead of raw data. In addition, participants’ preference scores for visualizations were significantly different under different motivations and heart rate data types. Based on these findings, we present design implications for interface designers to better visualize specific data on a smartwatch.