Late stage Hypertrophic Cardiomyopathy hearts develop atrial flutter/fibrillation.
There may be a cause not associated with the heart:
Hyperthyroidism (overactive thyroid), alcohol use, pulmonary embolism (a blood clot in the lungs), pneumonia
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But most commonly, atrial fibrillation occurs as a result of some other cardiac condition (secondary atrial fibrillation).
Heart valve disease: This can be something you are born with or be caused by infection or degeneration/calcification of valves with age. Enlargement of the left ventricle walls (left ventricular hypertrophy). Coronary heart disease (or coronary artery disease): This results from atherosclerosis, deposits of fatty material inside the arteries that cause blockage or narrowing of the arteries. High blood pressure (hypertension.
Cardiomyopathy (disease of the heart muscle) leading to congestive heart failure.
Sick sinus syndrome (improper production of electrical impulses because of malfunction of the SA node).Pericarditis (inflammation of the sac surrounding the heart).