['The objective was to evaluate the prevalence of paroxysmal atrial fibrillation (PAF) in patients with heart failure (HF) due to systolic dysfunction.', 'We included 79 patients (age 68 years, LVEF 30%) with HF and sinus-rhythm (SR) referred to a HF outpatient clinic. A 48 hours Holter ECG and a follow-up ECG were performed. RESULTS. One patient had one episode of PAF. Thirty-two (41%) patients had episodes of irregular atrial runs (AR). The numbers of QRS complexes during AR were 7.2+/-2.9 (mean+/-SD). Patients with AR were older than patients with SR, p =0.02 and more often of female sex, p =0.04. Multivariate logistic regression analysis showed that age and female sex were independently correlated with AR with adjusted OR of 1.1 (per year, 95% CI 1.02-1.14, p =0.01) and 4.0 (1.05-15.07, p =0.04), respectively. The presence of AR did not predict development of new-onset AF.'] Is paroxysmal atrial fibrillation uncommon in outpatients with chronic heart failure?