Abstract Left atrial (LA) enlargement is a common and early feature of cardiac involvement in the natural history of obesity and arterial hypertension (AH). Mechanisms involved in this process are cumulative, and partly shared, thus separating and balancing their contributions is challenging. In a proportion of patients referred for coronary artery calcium (CAC) scoring, these clinical entities are present. The LA volume (LAV) is relatively easy to quantify from a CT scan. Measured LAV values can be misleading unless constitutional parameters (height (h) or body size area (BSA), are considered. We introduced a new indexing parameter, consisting of height and the difference between numerical values of height and BSA. In the "ideal human", the difference is zero. Any deviation from this value determines the share of body mass regardless of height. Aim We hypothesize that a novel indexation approach allows for earlier detection of the increased LAV in normotensive and AH patients considering the body mass index. Method We retrospectively analyzed CT data from 2535 patients, 1658 w (64±10 ys), and 876 m (aged 6±11ys), with CAC scoring over the last 15 years The LAV was determined by using commercially available software. The raw and indexed (for h, BSA, and the novel parameter [h+ (h-BSA)]) LAV volumes were compared in patients with normal BMI (<25kg/msg), overweight (25-29.9), and obesity (≥30) who with normal blood pressure or with AH. Results The LAV was larger in high BMI categories than in normal BMI. In non-AH subjects, the LAV increased from an average of 71 ml (normal) to 80 ml (overweight) and 90 ml (obese). In AH, the LAV increase showed a similar trend of averages (77, 88, 94 ml, F=2.59,p<0.01). Indexing LAVs were non-concordant, as shown in Figure. Thus, one can recognize that LAV normalization for the new index has brought the differences most evident and persuasive. In normal BMI, indexation ways did not significantly affect the LAV estimation. Whilst the body weight increased, no difference could be recognized for values indexing for BSA (red). The LAV indexation for height (blue) cannot help diagnose its increase in obesity. The distinguishing strength can be seen while using the [h-(h-BSA)] denominator (green). It indicates that in any scenario, body mass gain plays a greater role in the LAV increase than AH does. Conclusions Body mass is a more important factor that is associated with LAV than AH.. Common methods of LAV indexing, especially referred to as BSA, introduce errors leading to values mimicking normality in non-healthy people and should be forbidden. The proposed indexation way can help overcome the observed discrepancies and support early recognition of the consequences of obesity and hypertension.