When Beta Blockers Do More Than Slow the Heart Beta blockers reduce heart rate and blood pressure by blocking beta-adrenergic receptors. With long-term use, that same mechanism can affect energy, circulation, exercise capacity, and sexual function in some people. ⚡ Fatigue Lower heart rate and contractility reduce cardiac output. In some patients this means less oxygen delivery to tissues, leading to persistent tiredness. Lipophilic beta blockers that enter the brain may further worsen fatigue.