Complications. When the tissues of the heart are devoid of oxygen, damage will ensue within about 30 minutes. Unstable angina exhibits complications that can be life threatening such as severe abnormal heart rhythms or arrhythmias, a heart attack, or what is called sudden cardiac death. Variant angina carries dangerous complications such as episodic disabling pain, arrhythmias or severe abnormal heart rhythms, heart attack, sudden cardiac arrest, sudden cardiac death, and atrioventricular block or a lack of electric conduction within the path between the atrium and the ventricle. Frequently occurring stable angina that is not diagnosed and treated in a timely manner by a physician can easily advance on to either unstable or variant angina, and induce the complications that come with each of them respectively.