Purpose: High blood pressure (BP) is a well-known risk factor for atrial fibrillation (AF), but a single BP measurement may provide limited information about AF risk in older adults. We evaluated whether longitudinal measures of BP were associated with subclinical arrhythmias after adjustment for more conventional BP measures such as a single cross-sectional BP value. Methods: This study included 1,256 Multi-Ethnic Study of Atherosclerosis (MESA) and 1,948 Atherosclerosis Risk in Communities study (ARIC) participants who underwent extended ambulatory electrocardiographic monitoring and who were free of clinically-detected cardiovascular disease, including AF. Using BP measurements from six exams (2000-2018 in MESA, 1987-2017 in ARIC), we examined cross-sectional BP at the most recent exam, individual long-term mean BP from exams 1-5, BP trend during exams 1-5, and visit-to-visit variability during exams 1-5 in systolic BP (SBP) and pulse pressure (PP) for each participant. Logistic regression models were used to examine BP exposures in relation to subclinical AF and linear regression models were used to examine BP exposures in relation to frequency of supraventricular ectopy. Models adjusted for participant demographics, height, weight, diabetes, antihypertensive medication use and cross-sectional BP. Results from each study were combined with inverse variance-weighted meta-analysis. Results: At Exam 6, the mean age was 73 years in MESA and 79 years in ARIC, and 4% had subclinical AF. A 10 mmHg higher cross-sectional SBP and a 10 mmHg higher cross-sectional PP were associated with less AF (odds ratio [OR] SBP 0.86, 95% confidence interval [CI] 0.76, 0.96 and OR PP 0.73, 95% CI 0.63, 0.84). In contrast, a 4 mmHg higher visit-to-visit variability in SBP was associated with a greater prevalence of subclinical AF (OR 1.20, 95% CI 1.02, 1.38) and with a greater frequency of premature atrial contractions/hour (8%, 95% CI 1%, 15%). For PP as well, a 4 mmHg higher visit-to-visit variability was associated with a greater prevalence of AF (OR 1.18, 95% CI 1.00-1.37). In addition, a 10 mmHg higher long-term mean PP was associated with a greater prevalence of subclinical AF (OR 1.36, 95% CI 1.08-1.70). Conclusion: Our results indicate that information on BP assessed longitudinally for several years, especially visit-to-visit BP variability, is associated with a greater prevalence of subclinical atrial arrhythmias, while cross-sectional BP values alone were not associated with a greater prevalence of subclinical atrial arrhythmias. Prior longitudinal BP assessment, rather than current BP, may be more helpful in identifying older adults who are at higher risk of atrial arrhythmias.