On Sunday night, Tamil Nadu Chief Minister J Jayalalithaa suffered a cardiac arrest, a condition where the heart unexpectedly stops beating. To keep a flow of oxygenated blood running to her vital organs, the Apollo hospital in Chennai put her on ECMO, or extra-corporeal membrane oxygenation, a system that mimics the functions of the lung and heart.

The video below explains how the machine works.

The video points out how ECMO can keep a patient alive provided that the patient’s lungs and heart, which are being given a break by the system, heal at the same time. However, doctors say that patients who are put on this machine have only a 50% chance of survival.

Jayalalithaa’s critical health status has created a tense atmosphere in Tamil Nadu. It came a few hours after her party, the All India Anna Dravida Munnetra Kazhagam, claimed that her condition had gradually improved over the past two weeks. The 68-year-old politician was admitted to hospital on September 22, suffering from fever and dehydration.