Baroreceptors in the left ventricle, aortic arch and carotid sinus detect the low cardiac output (low blood pressure) and notify the medulla which in turns stimulates the sympathetic nervous system. The SNS stimulates the release of the catecholamines epinephrine and norepinephrine, which causes vasoconstriction and leads to increased afterload, increased blood pressure and increased heart rate. This increases the work load of the heart and causes hypertrophy and dilation of the left ventricle and further impairs contractility. Also, the catecholamines cause direct toxic effects to the myocytes and induce myocyte apoptosis, thus causing more damage to the heart.