Clinical reminders can promote adherence with evidence-based clinical guidelines, but they may also have unintended consequences such as alert fatigue, false alarms and increased workload, which cause clinicians to ignore them. The described clinical reminder system identifies patients eligible for primary prevention of cardiovascular diseases and lets the physician to choose which patients will be included in the reminders intervention. We analyzed data of 87,165 visits of 35,699 patients and evaluated factors which may affect clinicians' decision to enroll patients to the intervention. The physicians included most of the patients suggested for inclusion (85.7%). Yet, they skipped the enrollment suggestion in 62.6% of the visits. Patients with a cardiovascular disease, dyslipidemia, diabetes, or hypertension were more likely to be included in the intervention, while older patients were less likely to be included. Insights regarding the usability of clinical reminders are discussed.