The mechanisms causing cardiac arrest due to acute pulmonary embolism mainly encompass several aspects. One is a large-scale acute extensive pulmonary embolism, which prevents the blood from being ejected from the right heart, potentially leading to acute right heart failure. At this time, the entire body's blood circulation will encounter issues. Another scenario is that following the pulmonary embolism, it causes severe hypoxia. This hypoxia can lead to oxygen deficiency in all organs of the body, including the heart. The coronary arteries that supply nutrients to the heart can also become ischemic. Both of these factors can cause the heartbeat to lead to sudden cardiac arrest. These are the primary mechanisms that can cause a sudden stop in the heartbeat.