How stress damages the heart

It is known that long term stress can cause fatal heart attacks and strokes, but scientists have never known why. Stress triggers our so-called ‘fight or flight’ mechanism which sends a surge of adrenalin to help the heart pump harder and increase blood flow to enable the body to fight or run when encountering a perceived threat.
But new research suggests that stress also sends the immune system into overdrive, increasing white blood cells and worsening inflammation in the arteries. And that can cause huge problems if arteries are already thickened with plaque. When damaged arteries become more inflamed they produce lesions which can break away, leaving an open wound which blood platelets and clotting proteins rush to fill.
A clot can enlarge in a matter of moments and if it completely obstructs the artery, will cause a heart attack. Dr Matthias Nahrendorf and his team at Massachusetts General Hospital and Harvard Medical School discovered that medical residents who were regularly exposed to chronic stress had a huge white blood cell counts. They also found that when mice are stressed, the stem cells in their bone marrow were activated and produced large numbers of white blood cells (leukocytes). 
Where mice already had thickened arteries (atherosclerosis) the blood cells increased inflammation and caused the same lesion-like plaques to form which rupture in humans and cause heart attacks. “Exposure to psychosocial stress is a risk factor for many diseases,” said Dr Nahrendorf.