Strokes happen when a blood vessel ruptures or becomes blocked, depriving the brain of its normal blood supply. The brain needs oxygen and glucose to function properly, but it doesn’t have much space to store those substances. It gets oxygen and glucose from circulating blood. Most strokes are caused by an embolus, which is a blood clot that develops somewhere in the circulatory system and then dislodges, traveling to a blood vessel in the brain. The clot interrupts blood flow and causes surrounding tissue to die. Strokes can be associated with Cushing’s disease, Rocky Mountain Spotted Fever, diabetes mellitus, heart disease, kidney disease and thyroid disease. Internal parasites, ruptured blood vessels, blood clots, tumors, blunt trauma to the head and ingestion of poisons can also contribute to strokes. Sometimes, strokes happen for no recognizable reason. How a stroke affects a dog depends on the location and extent of blood vessel bleeding or blockage. Most strokes happen suddenly. Affected dogs may have a head tilt, balance problems, weakness, disorientation and vision impairment. They also may become paralyzed and lose consciousness.