Syncope is the medical term for fainting.  It is a temporary loss of consciousness caused by insufficient blood flow, and thus inadequate oxygen supply to the brain, most commonly due to a drop in blood pressure.   While almost always frightening, it can be indicative of serious life-threatening abnormalities of the heart but often is due to conditions that are totally benign.  If it occurs, One should seek proper medical evaluation immediately. Depending on the cause, many people have warning signs prior to faintings such as lightheadedness, dizziness, loss of vision (“blacking out”), general weakness, nausea, perspiration, chest pain, shortness of breath or palpitations.  Bystanders might note that the person who fainted appear pale due to reduced blood flow to the head and body. Cardiac causes Arrhythmias Syncope can be due to abnormally fast, slow or irregular heartbeats (arrhythmia), where the heart is unable to deliver adequate blood flow to the brain.  If the heart rate becomes very slow due to degeneration of the intrinsic electrical system of the heart, one might need a pacemaker.  Rarely, some medications can slow the heart rate enough to lead to syncope.  Fainting can also occur due to very fast and irregular arrhythmias such as atrial fibrillation or supraventricular tachycardia, both of which are from abnormalities in the upper chambers of the heart and, by themselves, are not life-threatening.  If the heart rate goes fast enough, the heart is unable to pump blood effectively and blood pressure drops enough to lead to syncope.  Some people can be prone to faint due to their heart going too fast at times and too slow at other times, a condition called tachycardia-bradycardia syndrome. Syncope can also be due to ventricular tachycardia which occurs in the lower chambers of the heart and can be due to very serious underlying heart disease.  It can be a signs of coronary artery disease with inadequate blood flow to the heart muscle including from a heart attack or a heart muscle problem itself.  It is important to make sure that someone who has fainted is not at risk of ventricular tachycardia because this arrhythmia can lead to ventricular fibrillation and sudden cardiac death. Structural heart disease Significant heart valve disease can also lead to syncope, most commonly aortic stenosis.  Much less frequent causes in this day and age would include mitral stenosis and tumors within the heart, even otherwise benign tumors such as atrial myxomas.  Blood clots than form in the legs and travel through the heart to the lungs can cause syncope if they are large enough. Primary blood pressure problems If blood pressure drops enough, inadequate blood flow to the brain can occur, leading to syncope.  This is known as hypotension and can be due to significant dehydration, excessive bleeding or too much blood pressure medication.  Some people have inadequate “communication” between their blood vessels, heart, and brain so that when they stand, an adequate and stable blood pressure is not maintained and leads to fainting.  This is due to orthostatic or postural hypotension and is more common in diabetics.  As people age they are more prone to this especially in hot weather or with mild dehydration (like inadequate fluid intake). Vasovagal Syncope This is the medical term for a fainting episode in an otherwise healthy person in a particular situation.  It is also referred to as situational syncope and when it occurs repeatedly in someone is known as vasodepressor or neurocardiogenic syncope.  It usually occurs during uneasy, scary or embarrassing situations, or during blood drawing, coughing, urination or defecation.  It could be more likely to occur if the patient is relatively dehydrated, exposed to extreme heat, standing for a long period of time, sleep deprived, or under a lot of stress.  After a vasovagal episode, it is not uncommon for the person to have cold or clammy skin. Whatever the cause, in vasovagal syncope, there is less blood in the upper body when the person is standing. Blood is pooling in the lower body and can be worsened if the person is dehydrated or has had some alcohol which dilates blood vessels. The heart responds by more forcefully beating to make up for the lack of blood in its own chambers, but this overstimulation of the heart activates the parasympathetic part of the nervous system which is responsible for bringing down the heart rate and blood pressure. Clinical evaluation The majority of syncopal episodes are classified as vasovagal.  If the patient is otherwise healthy, they usually have a favorable prognosis.  If they have underlying cardiac disease, there is a much higher likelihood of a serious cause and the need for more extensive medical and cardiac evaluation.  Cardiologists are often asked to evaluate patients with syncope, which usually includes an electrocardiogram (EKG) but whether further cardiac testing such as a Holter monitor, event recorder, stress test or echocardiogram is necessary depends on the patient’s profile, their clinical history and physical exam and whether they are having recurrent episodes.