The Use of Point-of-Care Ultrasound (POCUS), Transthoracic Echocardiography (TTE), and Transesophageal Echocardiography (TEE) in Cardiac Arrest and Acute Coronary Syndrome Patients Studies have shown that POCUS can rapidly change the management in nearly 80% of cases in emergency settings, particularly in environments such as war zones and disaster relief. TTE is highly sensitive in diagnosing acute coronary syndromes and can effectively rule out myocardial infarction. In cardiac arrest patients, TTE assists in determining cardiac activity and identifying reversible causes, such as pericardial tamponade and pneumothorax. However, TTE can be affected by suboptimal image quality due to factors like chest compression in out-of-hospital cardiac arrest (OHCA) patients. In Taiwan's emergency medical system, EMT-Ps (paramedics) undergo approximately one year of training, which enables them to provide emergency care, including ultrasound examinations, before hospital arrival. Research on pre-hospital cardiac arrest has shown that most ultrasound applications can be completed within 3 minutes and do not significantly increase on-scene time. TEE, though advantageous for its high-quality imaging and ability to reduce interruptions during chest compressions, faces challenges in pre-hospital emergency applications due to specialized training and equipment requirements. However, a study in Vienna, Austria, demonstrated that TEE could be performed and yield high-quality images in most pre-hospital cases, with an average examination time of 5.1 minutes. Several hospitals in Taiwan have begun training personnel in TEE, emphasizing the importance of establishing TEE image registries for large-scale, effective research analysis. However, these efforts also face challenges related to resources and collaboration. The research team has over three years of experience using TEE in the emergency department to examine OHCA patients, and a three-year study will be conducted to validate the efficacy of pre-hospital TEE in cardiac arrest patients.