A monitoring system for cardiac operations with cardiopulmonary bypass comprising: a processor operatively connected to a heart-lung machine; a pump flow detecting device connected to a pump of the heart-lung machine to continuously measure the pump flow value and send it to the processor; a hematocrit reading device inserted inside the arterial or venous line of the heart-lung machine to continuously measure the blood hematocrit value and to send it to the processor; a data input device to allow the operator to manually input data regarding the arterial oxygen saturation and the arterial oxygen tension; computing means integrated in the processor to compute the oxygen delivery value on the basis of the measured pump flow, the measured hematocrit value, the preset value of arterial oxygen saturation, and the preset value of arterial oxygen tension; and a display connected to the processor to display in real-time the computed oxygen delivery value.