When sympathetic activation is low, these drugs have modest effects. However, when sympathetic activation is high, such as during exercise and stress, beta blockers attenuate the expected increase in heart rate, and diminish cardiac output. Blockade of vascular Beta 2 receptors results in increased total peripheral resistance. Blood flow to most organs other than the brain is reduced. With long term use total peripheral resistance returns toward normal by unclear mechanisms.
Beta blockers tend to decrease the capacity to work.
Exercise performance is impaired less by selective Beta 1 blockers. Beta blockers have important effects on cardiac rhythm and automaticity. They reduce the sinus rate, decrease the rate of depolarization of ectopic pacemakers, and slow conduction in the atria and AV node. Lots more on this topic during lectures on antiarrhythmic drugs. Beta blockers do not lower blood pressure in normal man, however they do reduce blood pressure in hypertensive man.