BACKGROUND/AIMS: Low arterial blood pressure is recognised as a distinctive factor in the hyperdynamic circulation in cirrhosis. 24-hour monitoring of the blood pressure and heart rate has recently revealed a reduced circadian variation with relation to liver function. However, associations with other clinical and haemodynamic characteristics have not been investigated and the aim of the present study was to identify splanchnic and systemic determinants of the 24-h blood pressure and heart rate in cirrhosis. METHODS: The variables were measured by an automatic ambulant device for monitoring blood pressure and related to the results of an invasive haemodynamic investigation, including measurements of intra-arterial blood pressure (9.00-11.00 h) in 37 patients with cirrhosis. RESULTS: The 24-h blood pressures were significantly lower and the heart rate was significantly higher in patients with cirrhosis than in matched controls (p < 0.05-0.001). To identify determinants of 24-h or intra-arterial blood pressures and heart rate, pertinent variables were included in a multivariate regression model. This model revealed that independent determinants of a low 24-h arterial blood pressure were a high post-sinusoidal resistance, a low plasma volume, a short central circulation time, and the presence of ascites. In contrast, a low intra-arterial blood pressure was determined by a low serum sodium, a low haemoglobin, and a high cardiac output. Diuretic treatment did not influence this model. CONCLUSIONS: Although the 24-h blood pressure and the intra-arterial blood pressure were determined by different variables, the overall results indicate that abnormalities in both splanchnic and central haemodynamics and sodium-water retention are important in the pathophysiology of arterial hypotension in patients with portal hypertension.