The use of point-of-care ultrasound of the heart is becoming more widespread. A variety of users have joined traditional users of cardiac ultrasound, cardiologists, and are imaging their patients in real time at the point of care. Patients with undifferentiated shock, hypotension, chest pain, or dyspnea are ideal candidates for focused cardiac ultrasound (FOCUS). In addition, any patient in whom the diagnosis of pericardial effusion or tamponade, pulmonary embolism, or left ventricular dysfunction is suspected would benefit from FOCUS. Of particular importance is the use of FOCUS to rapidly determine the etiology of cardiac arrest. This review will detail the indications, techniques, and limitations of FOCUS in these patients.