© The Author 2014. Published by Oxford University Press on behalf of the British Society for Rheumatology. All rights reserved. Objective. Increased left ventricular (LV) wall thickness/internal diameter ratio (relative wall thickness) was recently reported in RA patients. The aim of this study was to assess the association between LV relative wall thickness and RA disease activity. Methods. Clinical and echocardiographic data from 129 RA patients without established cardiovascular disease and 102 controls were used. RA disease activity was assessed by different composite scores and active RA defined by the Simplified Disease Activity Index (SDAI) level exceeding the cut-offfor remission (SDAI textgreater 3.3). Results. The RA patients were on average 61.3 years old, 77% were women and 67% had active RA (SDAI textgreater 3.3). Patients with active RA had greater LV relative wall thickness and included more patients with treated hypertension (all P textless 0.05), but had LV mass index and blood pressure comparable to patients in remission. Having active RA by the SDAI score (b = 0.20, P = 0.008) was also independently associated with greater LV relative wall thickness after adjusting for systolic blood pressure, wall stress, age and sex in a multivariate model. This association was robust also in secondary models including other disease activity composite scores such as the Clinical Disease Activity Index and 28-joint DAS. Conclusion. Among RA patients, higher disease activity was independently associated with greater LV relative wall thickness, reflecting subclinical heart disease. The findings point to the importance of disease activity control in RA patients to prevent progression to clinical heart disease.