Description: fainting, or loss of consciousness.  Generally occurs suddenly, though often there is a period of warning.

Some causes related to cardiovascular disease: Several cardiac disorders can cause syncope, including obstruction of the heart valves and cardiac tumors.  However, the most common cardiac cause of syncope is cardiac arrhythmias.

Some causes related to other disorders: Numerous other disorders can cause syncope including neurological disease, metabolic disease, and a common condition known as vasovagal syncope.

Significance: Syncope is always potentially dangerous, because injury can occur if one faints suddenly.  Cardiac causes of syncope are inherently life-threatening, and need to be characterized rapidly and treated aggressively.  Syncope therefore always requires a full medical evaluation. When syncope occurs for the first time after heart disease has set in,  it should be treated as a medical emergency until a potentially lethal arrhythmia has been ruled out.

Links to syncope 
Links to cardiac arrhythmias