A doctor places an implantable cardioverter-defibrillator (also called an ICD) in the chest. The ICD has one or two wires called leads. These leads go into the heart through the subclavian vein (transvenous). Some ICDs have a lead that is placed under the skin so that it lies near your heart (subcutaneous). The ICD checks the heartbeat for an abnormal rhythm. If the ICD senses an abnormal heart rhythm, it sends out either electrical pulses or a shock to fix it.