Per the European Union legal framework, a medical device is an apparatus that is used in diagnosis, prevention, or treatment of diseased conditions where its mode of action is not through chemical action in a patient’s body. Medical devices consist of enormous variations with regard to their sophistication and scope of use, which ranges from tongue depressors to medical robots and cardiac pacemakers. Biomedical engineering involves fundamental aspects of the device production including designing, system analysis, and practical application. This is in line with ensuring that quality and reliable devices. This paper seeks to highlight defibrillators as medical devices with regard to their history, scope of application and safety aspects of the device in terms of human factors engineering. It is estimated that about 30,000 people in the United Kingdom experience cardiac arrest away from the hospital annually and they are assisted by medical emergency response units (Resuscitation Council, 2010). Such assistance is facilitated by the availability of portable medical devices, which prove essential in the delivery of the critically required services. Among the crucial devices required in relieving the effects of cardiac arrest is the defibrillator. Defibrillators are apparatus, external or implanted, that deliver an electric shock to the heart via the chest cavity in order to restore normal heart rhythms. Defibrillators function by delivering a joust of electric current to the heart in order to polarise the muscles and nerve cells, allowing them resume a normal rhythm (Street, 2012). Implanted Cardioverter Defibrillator (ICD) constantly monitors the heartbeat rate as well as its rhythm to detect abnormal and life threatening rhythms, which on detection an electric shock is sent to the heart to restore a normal rhythm (Defibrillation, n.d). The device also works as a pacemaker to curb the effects of the electric shock, which slows down the rate of the heartbeat. The above is illustrative of a monitoring and feedback mechanism, where the defibrillators function based on signals taken from the patient after its analysis. Among the external defibrillator units are automated external defibrillators (AED), which automate the patient’s heartbeat rhythms for monitoring as electric shock is administered to normalise the rhythm. AEDs consist of in-built computer systems that examine the patient’s heartbeat in order to assess the need to administer defibrillation (Sciammarella, n.d.). One of the common causes of cardiac arrest is ventricular fibrillation, which is characterised by chaotic, unorganised electrical malfunction of the heart resulting in a less effective heartbeat (Khandpur, 2003). This chaotic electrical activity can be stopped and its effects reversed by the application of an electrical counter shock where heart assumes a normal and organised rhythm. Disorders in the generation of a normal pulse by the heart results irregular heartbeats manifested in arrhythmias. Abnormal automaticity and triggered activity are characteristic of conduction abnormalities that trigger ventricular tachycardia. In addition to the use of medication and surgical procedures in the management of arrhythmias, defibrillation comes in handy in resolution of ventricular tachyarrhythmia and atrial fibrillation. This is especially so for medical emergencies that occurs away from healthcare facilities.