A blood clot in the heart causes life-threatening consequences if it breaks off and travels to the brain, according to Mayo Clinic. A common cause of this type of blood clot is an irregular heart rhythm known as atrial fibrillation. Similarly, a blood clot in one of the arteries in the heart can cut off the oxygen supply to a portion of the heart muscle, causing a heart attack.
When atrial fibrillation occurs, the left upper chamber of the heart beats rapidly and ineffectively, causing blood to pool in the area, where it sometimes clots, explains the National Institute of Neurological Disorders and Stroke. If the clot breaks off and blocks a blood vessel in the brain, it deprives part of the brain of oxygen, and a stroke occurs. People with atrial fibrillation often have multiple strokes, many of which produce no symptoms. However, they sometimes lead to dementia over time. Treatment with blood-thinning medication helps prevent blood clots in this patient population and significantly reduces the risk of stroke.
Blood clots in the coronary arteries are usually the result of atherosclerosis, a condition in which a tacky substance known as plaque builds up inside the arteries in the heart, explains the National Heart, Lung and Blood Institute. This plaque sometimes ruptures within the blood vessel, causing a clot to form. If the clot obstructs blood flow sufficiently, the heart muscle begins to die, producing the symptoms of a heart attack. Without prompt medical treatment, many heart attack victims die.