Acute pulmonary embolism (APE) presents with a broad clinical spectrum ranging from an even asymptomatic course to sudden cardiac death. Because APE is potentially life-threatening every suspicion of APE has to be clarified promptly by validated diagnostic algorithms. On the basis of the patients haemodynamic instability high-risk APE and non-high-risk APE is differentiated. Based on the presence of shock or hypotension every patient with suspicion of APE should promptly be stratified as high-risk APE or non-high-risk APE. There is a considerable difference in the diagnostic and therapeutic algorithms between high-risk and non-high-risk APE. In suspicion of high-risk APE the patients require immediate diagnosis by multidetector CT or echocardiography and immediate recanalization of the occluded pulmonary arteries by thrombolysis or embolectomy. In haemodynamically stable patients sequential diagnostic workup and prompt therapeutic anticoagulation is recommended.