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Subarachnoid blockade is defined as a temporary interruption of nerve impulse transmission produced by injecting of a local anesthetic into the subarachnoid space. The only reason for the clinical effects of subarachnoid anaesthesia on the cardiovascular system is a preganglionic sympathetic block, which affects all the haemodynamic parameters determining the blood pressure. The decrease in blood pres­sure following subarachnoid blockade is caused by a decrease in both cardiac output and in peripheral resistance. The decrease in cardiac output is due to a decrease in preload sec­ondary to an increase in venous capacity lead­ing to a lower filling pressure to the heart. During high subarachnoid block the reduction in cardiac output is also caused by a decrease in heart rate and perhaps by a decrease in the contractility of the heart.