The purpose of this study was to examine the relationship between arterial hypertension (HTN), chronic heart disease (CHD), and selenium (Se) status. Blood and plasma Se concentrations and Se-dependent GSH-Px activities were determined in 40 patients (HTN = 20; CHD = 20) and 17 healthy volunteers aged 41 to 66 years. Whole blood and plasma Se concentrations were significantly lower in the patients with HTN (19.1% and 26.3%, respectively) and CHD (33.1% and 29.4%, respectively) compared with the values obtained in the controls. The hypertensive patients had lower plasma Se-GSH-Px (26.7%), and those with CHD had both lower whole blood (19.5%) and plasma Se-GSH-Px activities (30.2%). A significant positive correlation between plasma Se-GSH-Px activity and ejection fraction (EF) was found in patients with CHD. There were significant correlations between plasma and whole blood Se concentration, plasma Se concentration and Se-GSH-Px activity, and whole blood Se and Se-GSH-Px activity. Our results showed that hypertensive patients and those with CHD had lower Se levels compared with controls. We conclude that low Se content might be a risk factor for development of HTN and CHD.