The purpose of this single center, randomized clinical control trial is to determine that changing chest compression site during cardiopulmonary resuscitation according to the examination of the TEE could increase the level of end-tidal CO2, which represents the quality of cardiopulmonary resuscitation, or not in adult patients with non-traumatic out-of-hospital cardiac arrest while comparing to those who don't receive examination of transesophageal echocardiography during cardiopulmonary resuscitation.

Inclusion Criteria:

1. Age ≥ 20 years-old
2. Out-of-hospital cardiac arrest
3. Non-trauma

Exclusion Criteria:

1. Obvious signs of death appears, such as separation of head and body, rigor mortis, livor mortis, cankered corpse......etc.
2. Family members clearly express the willing of do not attempt resuscitation or patients who have registered advance care planning not to attempt resuscitation.
3. Patients not suitable for transesophageal ultrasound, such as patients with esophageal tumor, those whose probe cannot be placed......etc.
4. Received Extracorporeal CPR.
5. Achieving sustained ROSC before ED arrival

This is an open label study