PURPOSE: Atrial fibrillation (AF) is commonly associated with structural heart disease. Although heart failure (HF) has been proposed as a risk factor for stroke, the coexistence of the 2 diseases increases disproportionally the risk of thromboembolic events. Our objective was to conduct a systematic review to assess the effect of HF on the end points of stroke, systemic embolism (SE), or mortality in patients with AF. METHODS: A literature search was performed to identify studies that examined stroke/ SE in relation to AF and HF. Overall, 405 articles satisfied the preinclusion criteria. FINDINGS: In studies in which HF was based on a clinical diagnosis, HF independently increased stroke/SE in 5 of 13 studies, conferring 1.6- to 3.1-fold increase in risk. When HF was defined as impaired left ventricular (LV) function on echocardiography, the additive risk was evident in 4 of 6 studies, with 1.7- to 2.6-fold increase in the risk of stroke/SE. The data about HF with preserved ejection fraction were less robust, although a recent presentation with acute decompensated HF increased the risk of stroke/SE, irrespective of ejection fraction. IMPLICATIONS: LV systolic impairment as identified by echocardiography is an independent risk factor for stroke/SE, although the magnitude by which it increases the risk of stroke cannot be precisely quantified. Whether a clinical diagnosis of HF is a significant risk factor remains inconclusive, although when the diagnosis is certain (recent decompensation requiring hospitalization), it does seem to be a significant risk factor irrespective of LV systolic function.