Federal health regulators are warning the public that certain cardiac defibrillators recalled by Philips Healthcare may fail to deliver a needed shock in an emergency. Defibrillators are used by emergency responders and others to restore normal heart function in people suffering a heart attack. The FDA says an electrical problem with recalled Philips' HeartStart devices could cause them to fail to deliver a life-saving shock. Philips recalled three models of its HeartStart devices in September 2012 due to an internal electrical malfunction. The recall affects about 700,000 defibrillators sold between 2005 and 2012.