Final answer:
A short-acting beta blocker is a medication that blocks specific beta receptors in the body, improving cardiac function. However, not all beta blockers are B1 selective.
Step-by-step explanation:
A short-acting beta blocker is a type of medication that blocks beta receptors in the body. Beta blockers are commonly used to treat cardiovascular diseases by blocking the receptors associated with vasoconstriction and cardioacceleration. By blocking these receptors, the medication can prevent an increase in heart rate and improve cardiac function. However, it is important to note that beta blockers are not always B1 selective, meaning they may also affect other types of beta receptors.