OBJECTIVES: AF is the most common chronic cardiac arrhythmia worldwide and is an important risk factor for morbidity related mainly to an increased risk of cerebrovascular events and heart failure. This study examined the prevalence of comorbidities among patients receiving treatment for AF in 4 Latin America countries to convey a more comprehensive picture of the total disease burden. METHODS: For study purposes, co-morbidity was defined as the presence of one or more disorders in addition to a primary disease, or the effect of such additional disorders. A 3-step process was conducted in order to understand treatment patterns for patients suffering from AF: (1) health care assessment per country, (2) evaluate patient´s information and (3) data analysis to understand and determine treatment algorithms. Data were collected through 59 face-to-face interviews with cardiologists in Argentina, Brazil, Chile, and Venezuela.   RESULTS: Analysis per country suggested that, in Chile and Venezuela, 98% and 94% of patients, respectively, reported at least one co-morbidity. In Argentina this pattern was observed in 81% of the patients, whereas in Brazil this was 78%. Findings revealed that  the main 5 comorbidities associated with AF were: (1) Hypertension: LatAm 43%, Argentina 28%, Brazil 45%, Chile 43%, Venezuela 33%; (2) Dyslipidemia: LatAm 22%, Argentina 11%, Brazil 25%, Chile 21%, Venezuela 18%; (3) Diabetes: LatAm 13%, Argentina 8%, Brazil 11%, Chile 10%, Venezuela 18%; (4) Cardiopathies: LatAm 8%, Argentina 4%, Brazil 8%, Chile 8%, Venezuela 9%; and, (5) Thyroid disease: LatAm 7%, Argentina 4%, Brazil 3%, Chile 12%, Venezuela 9%. CONCLUSIONS: Overall, the analysis suggests that hypertension is the main co-morbidity associated with AF, followed by dyslipidemia and diabetes. The health burden carried by patients often extends far beyond AF. Physicians should carefully consider comorbidities and concomitant medications when managing patients.