Stopping the heart

During this procedure the patient is connected to the machine, venous blood being aspirated through cannuls through the right atrium into the heart-lung pump, while oxygenated blood is returned to the arterial circulation through a cannula in the ascending aorta. Preventing the function of the heart is not a very difficult process. When the heart-lung machine is activated and the blood is cooled and redirected into blood vessels, the body temperature is reduced to below 30⁰ C, and this lowers the heart rate and assists the heart to stop functioning. The actual stopping of the heart is performed by feeding a serum containing a concentrated solution of potassium ions into the coronary artery, which feeds the heart muscle. Potassium ions are normally found in the human body but in fixed proportion; potassium is an electrolyte which, if increased, causes defect in the heart's rhythm and may lead to ceasing the heart function. Feeding the coronary artery rapidly with rich potassium solution causes the heart to stop within a few seconds and allows the surgeon to perform operation on a non-functioning, motionless heart.

The heart should not be stopped from functioning for a long period, even if the heart-lung pump is performing the function of the heart successfully. Under normal conditions the pump cannot perform the whole duty of the actual heart and lungs. When the body temperature is reduced, there is reduction of functioning in many organs of the body to such an extent that they almost stop working, especially the brain.