Intermittent and chronic volume overload might contribute to the onset and progression of cardiovascular disease in patients who are undergoing maintenance hemodialysis (HD). Continuous monitoring of central hemodynamic variables may provide valuable information to improve volume control, particularly in patients with left ventricular dysfunction. Sixteen patients with end-stage renal disease who were undergoing long-term HD received an implantable hemodynamic monitor consisting of a subcutaneously implanted memory device and transvenous right ventricular (RV) lead with a pressure sensor. The implantable hemodynamic monitor continuously records heart rate, RV pressures, and estimated pulmonary arterial (PA) diastolic pressure, an estimate of left ventricular filling pressure. All patients underwent HD 3 times per week, and averages of rest hemodynamic values from the first, second, and third nights after HD during 12 weeks were analyzed. The third night always occurred after the weekend, when there was an extended interval between dialysis sessions. From the first night to the second night, RV systolic pressure increased by 10 +/- 8% (p <0.001), and estimated PA diastolic pressure increased by 16 +/- 14% (p <0.001). On the third night, RV systolic pressure increased by 14 +/- 12% (p <0.001), and estimated PA diastolic pressure increased by 23 +/- 18% (p <0.001) compared with the first night. In conclusion, the progressive pressure increments between dialysis sessions seen in this study suggest that the implantable hemodynamic monitor was a sensitive indicator for changes in volume load in patients who were undergoing HD treatment. The results also suggest that more frequent dialysis may avoid excessive pressure increase, but this needs to be investigated further in future studies.