Background. Arteriovenous (AV) fistulas used for hemodialysis access may affect cardiac load by increasing the preload while decreasing the afterload. In dogs, AV fistulas have also been shown to affect coronary perfusion negatively. We investigated the net effect of AV fistulas on cardiac oxygen supply and demand. Methods. Aortic pressure waves were reconstructed from finger pressure recordings obtained on the nonfistula arm using a wave-form filter. Changes in systolic, mean, and diastolic aortic pressure were calculated, together with changes in heart rate (HR), stroke volume (SV), cardiac output (CO), and systemic vascular resistance (SVR) during a 60- second compression of AV fistulas in 10 patients. Changes in cardiac supply and demand were estimated by calculating the area under the aortic pressure curve during diastole [diastolic pressure time index (DPTI)] and systole [systolic pressure time index (SPTI)], respectively. Results. During fistula compression, systolic, mean and diastolic pressure increased by 4.2 ± 4.3, 2.6 ± 3.0, and 2.8 ± 2.9 mm Hg (mean ± SD, all P < 0.05). The HR decreased by 3.8 ± 2.5 beats per minute (P < 0.01), and SV decreased 3.7 ± 6.1% (NS). CO decreased 9.4 ± 8.6%, and SVR increased 14.3 ± 11.7% (both P < 0.05). The SPTI increased by 1.5 ± 1.5 mm Hg · sec (P < 0.01), and the DPTI increased by 7.6 ± 8.1 mm Hg · sec (14.8% increase, P < 0.05) during compression. The ratio of supply and demand (DPTI/SPTI) improved by 13.5 ± 13.0% (P < 0.01) when the fistula was compressed. Conclusion. AV fistulas have a small effect on left ventricular oxygen demand, but decrease cardiac oxygen supply considerably.