What causes Heart Palpitations ? 

Many things can cause palpitations. You may have these feelings even when your heart is beating normally or somewhat faster than normal.
                
Most palpitations are harmless and often go away on their own. However, some palpitations are signs of a heart problem. Sometimes the cause of palpitations can't be found.
                
If you start having palpitations, see your doctor to have them checked.
                
Causes Not Related to Heart Problems
                
Strong Emotions
                
You may feel your heart pounding or racing during anxiety, fear, or stress. You also may have these feelings if you're having a panic attack.
                
Vigorous Physical Activity
                
Intense activity can make your heart feel like its beating too hard or too fast, even though it's working normally. Intense activity also can cause occasional premature (extra) heartbeats.
                
Medical Conditions
                
Some medical conditions can cause palpitations. These conditions can make the heart beat faster or stronger than usual. They also can cause premature (extra) heartbeats.
                
Examples of these medical conditions include:
                
An overactive thyroid
                
A low blood sugar level
                
Anemia
                
Some types of low blood pressure
                
Fever
                
Dehydration (not enough fluid in the body)
                
Hormonal Changes
                
The hormonal changes that happen during pregnancy, menstruation, and the perimenopausal period may cause palpitations. The palpitations will likely improve or go away as these conditions go away or change.
                
Some palpitations that occur during pregnancy may be due to anemia.
                
Medicines and Stimulants
                
Many medicines can trigger palpitations because they can make the heart beat faster or stronger than usual. Medicines also can cause premature (extra) heartbeats.
                
Examples of these medicines include:
                
Inhaled asthma medicines.
                
Medicines to treat an underactive thyroid. Taking too much of these medicines can cause an overactive thyroid and lead to palpitations.
                
Medicines to prevent arrhythmias. Medicines used to treat irregular heart rhythms can sometimes cause other irregular heart rhythms.
                
Over-the-counter medicines that act as stimulants also may cause palpitations. These include decongestants (found in cough and cold medicines) and some herbal and nutritional supplements.
                
Caffeine, nicotine (found in tobacco), alcohol, and illegal drugs (such as cocaine and amphetamines) also can cause palpitations.
                
Causes Related to Heart Problems
                
Some palpitations are symptoms of arrhythmias. Arrhythmias are problems with the rate or rhythm of the heartbeat. However, less than half of the people who have palpitations have arrhythmias.
                
During an arrhythmia, the heart can beat too fast, too slow, or with an irregular rhythm. An arrhythmia happens if some part of the heart's electrical system doesn't work as it should.
                
Palpitations are more likely to be related to an arrhythmia if you:
                
Have had a heart attack or are at risk for one.
                
Have coronary heart disease (CHD) or risk factors for CHD.
                
Have other heart problems, such as heart failure, heart valve disease, or heart muscle disease.
                
Have abnormal electrolyte levels. Electrolytes are minerals, such as potassium and sodium, found in blood and body fluids. They're vital for normal health and functioning of the body.