Underlying medical conditions may be the cause of heart palpitations. These include: overactive thyroid; anemia; low blood sugar; low potassium; dehydration; high temperature and fever; loss of blood; shock; low oxygen or carbon dioxide levels in the blood; Hormone changes. Hormonal changes are another possible cause of heart palpitations. Changes in hormone levels may result from: menstrual periods; pregnancy; menopause; Heart conditions. Palpitations can also be caused by heart conditions, including: arrhythmias (abnormal heart rhythms) coronary artery disease or a heart attack; heart valve problems; heart failure