Abdominal inferior vena cava pressure was compared to intrathoracic central venous pressure in 30 adults admitted in an intensive care unit following coronary artery bypass grafting. Mean pressures were obtained during controlled ventilation with a positive end expiratory pressure (PEEP) of zero and 10 cmH2O respectively, and during spontaneous breathing as well. Ninety measurements were obtained. Limits of agreement between intra-abdominal and intrathoracic cava pressures were below 2.5 mmHg in all cases. In this study, inferior vena cava pressure has predicted central venous pressure in adults during both controlled and spontaneous ventilation.