Atrial fibrillation (AF) is one of the most frequent arrhythmias and is an important cause of morbidity and mortality, mainly associated with increased risk of stroke. Left ventricular hypertrophy (LVH) is a progressive, silent pathology and represents a manifestation of early cardiac damage caused by arterial hypertension, is considered a risk marker, essentially of AF and stroke and especially increases the risk of morbidity, acute myocardial infarction and ischaemic disease. This is an exploratory cross-sectional study of a non-probabilistic sequential sample, representative of the population of Trás-os-Montes who used primary care, aged 40 years or over. The prevalence and incidence of AF and LVH were based on electrocardiograms classified by cardiologists. Anthropometric and clinical data were collected to characterise the population. The electrocardiogram is the test indicated for diagnosing AF and LVH in primary care. Because of the high values obtained, it is important todevelop strategies to control risk factors, since AF and LVH increase the risk of stroke.