IntroductionAtrial fibrillation (AF) is the most frequent arrhythmia. Its prevalence increases with age. Atrial flutter is a less common and analogous arrhythmia. The treatment of the elderly patient is not always the same as the recommended one by the different scientific societies. ObjectivesDescribe the anticoagulant treatment of patients aged 75 years or older who was admitted in the Internal Medicine service for any reason, with previously known AF or atrial flutter or diagnosed at the time of admission, during the months of April, May and June 2018. Describe the mortality in this admission and in the subsequent follow-up and assess the importance of baseline factors in the future of these patients. Material and methodsProspective observational study of consecutive patients admitted between April 1st and June 30th, 2018 in the Internal Medicine service of a second-level hospital in the province of Valencia. Categorical variables were described with percentages, and continuous numerical variables with mean, standard deviation, minimum and maximum. Comparisons between categorical variables were made with the Chi-squared test, and the comparison between categorical and numerical variables with Student's t tests or ANOVA. ResultsIn this time interval, 125 patients were admitted, 115 with AF and 10 with atrial flutter. Of these, 111 (80.8%) were anticoagulated upon admission (78 with vitamin K antagonists (VKA) and 23 with directly acting oral anticoagulants (DOAC). 13 patients (10.4%) died during this hospital admission. In the next 2 years, 72 patients (64.3%) had readmissions in the hospital and 70 died (62.5). There were 12 admissions (9.6%) and 8 readmissions (11.1%) due to significant bleeding. Thirty-three patients (42.3%) anticoagulated with VKA were found in the therapeutic range at the time of admission. Survival of anticoagulated patients was greater than that of non-anticoagulated patients (median survival of 19.9 vs. 5.6 months), and higher in the group with VKA than with DOAC (median survival of 21.8 vs. 9.9 months). There were no significant differences in stroke or significant bleeding between the groups of patients taking VKA with high INR, normal or low INR or taking DOAC. ConclusionsThe medium-term mortality of this group of patients was high, although the mortality during admission was lower. Anticoagulation of these patients appeared to provide survival benefit and was not associated with significant bleeding complications.