beta blockers work by blocking beta adrenergic receptors, there are multiple types of beta adrenergic receptors in different types of tissue, for the heart, the main stimulants (when talking about stimulating increased heart rate/contractile force in response to catecholamine release) is the B-1 adrenergic receptor subtype, thus beta blockers that are more selective to blocking the effects (antagonising) B1 adrenergic receptors will be the most effective at slowing down heart rate/ reducing palpitations and/or arrhythmias.
Beta adrenergic receptors are the targets/ sites for catecholamines such as epinephrine (adrenaline), and I’m almost sure I spelled that wrong, and norepinephrine or however you spell it, blocking these receptors block the effects of ephineprine and however you spell the other one… thus beta blockers are also fantastic for reducing the physiologic side effects of anxiety, I find them immensely helpful for thus (anxiety is a vicious cycle, physiologic sides fuel phychological sides, and it’s a vicious loop until one can be cut off), thus yeetfloopity I have my beta-blocker for that and autonomic instability.
Alpha blocker… eh, there’s more tried and true ways to achieve an erection (I mean you can always try yohimbine (alpha 2 adrenergic receptor agonist), could relax smooth muscle and allow more blood flow, however if you’re looking to slow your heart rate… yohimnine isn’t a great choice lol, kinda counterproductive. Ever try a PDE5 inhibitor, I don’t have ED, but I’ve used Cialis before as I’m an irresponsible moron sometimes and it’s fucking awesome. (just make sure you’re BP isn’t super low, for someone like me, experimenting with a vasodialating medication such as Cialis is actually quite dangerous).
I’m not qualified to give medical advice btw, so take what I say with a grain of salt. Dr Mr Dr Mr Dr Mr Dr Mr Dr Mr Sir Mr Dr Sir Professor Sir Sirrington is the person to ask about this for a more accurate response.