Some nebulae create their own light, which sometimes has a fluorescent appearance, while others only reflect the light from nearby stars. Nebulae are often seen around dying stars, and it's thought they may be a natural process that occurs when a star is nearing the end of its life. Nebulae resemble thin clouds that have less atoms per cubic inch than a cloud of smoke.
When there is not enough thyroid hormone, neither the heart nor the blood vessels can function normally. In hypothyroidism, the reduced level of thyroid hormone causes the heart muscle to pump less vigorously, and eventually to become weakened. In addition, the heart muscle cannot fully relax after each heart beat.
Common causes of abnormal heart rhythms (arrhythmias) or conditions that can lead to arrhythmias include: 1  Heart defects you're born with (congenital heart defects). 2  Coronary artery disease. 3  High blood pressure. 4  Diabetes. 5  Smoking.6  Excessive use of alcohol or caffeine. 7  Drug abuse.8  Stress.he cause of cardiomyopathy, a thickening or enlarging of the heart muscle, may depend on the type: 1  Dilated cardiomyopathy. 2  The cause of this most common type of cardiomyopathy often is unknown. 3  It may be caused by reduced blood flow to the heart (ischemic heart disease), infections, toxins and certain drugs.