A normal heart rate is 60 to 80 beats per minute. However, in certain conditions, the heart beat is accelerated. The major system involved in acceleration of heartbeat is sympathetic nervous system. It releases hormones like adrenaline and noradrenaline during stress or excitement. Exercise also stimulates sympathetic nervous system to accelerate the heartbeat. Apart from heartbeat, sympathetic nervous system and noradrenaline constricts blood vessels, goose bumps, sweating, increased blood pressure, dilation of pupil. Thus, the correct answer is 'Sympathetic nerves and noradrenaline.'

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