Imbalance between cardiac oxygen supply and demand may trigger cardiac events in already vulnerable hemodialysis (HD) patients. We studied the effect of ultrafiltration (UF) and HD in nine chronic HD patients by continuously measuring blood volume (BV; by Critline), blood pressure (BP; by Portapres), and changes in hemodynamics (Modelflow) during isolated UF (iUF) of 500 mL in 30 minutes and subsequent HD combined with UF (HD + UF). Aortic pressure was reconstructed from finger pressure. Changes in cardiac oxygen supply were assessed by calculating the area under the aortic pressure curve during diastole (diastolic pressure time index [DPTI]). Changes in cardiac oxygen demand were assessed by calculating systolic pressure time index (SPTI). BV decreased 4.0% +/- 1.8% during UF and 7.3% +/- 3.3% during HD + UF (both P < 0.01). Systolic BP did not change; diastolic and mean BP increased 11 +/- 7.4 and 11 +/- 8.4 mm Hg during iUF, respectively (both P < 0.01), and stabilized during HD + UF. Overall pulse pressure decreased 19 +/- 11.1 mm Hg (P < 0.01). Heart rate increased 13 +/- 11 beats/min (P < 0.01) and systemic vascular resistance increased 59% +/- 51% (P < 0. 01), whereas stroke volume and cardiac output (CO) decreased by 40% +/- 17% and 30% +/- 13%, respectively (both P < 0.01). Both cardiac oxygen supply (DPTI) and demand (SPTI) increased during iUF, and both decreased during HD + UF. By the end of the procedure, DPTI/SPTI ratio had increased 9% +/- 8% (P < 0.05). Changes in CO correlated closely to changes in BV. Despite large changes in hemodynamics during uncomplicated UF and HD, the balance between cardiac oxygen supply and demand (DPTI/SPTI ratio) did not decrease, but improved slightly.