Final answer:
Beta-blockers increase the ejection time by blocking the effects of adrenaline, leading to a slower heart rate and reduced contraction force, which can be therapeutic in certain cardiovascular conditions.
Step-by-step explanation:
β-blockers generally increase the ejection time during the cardiac cycle by decreasing heart rate and contractility by blocking the effects of adrenaline.
β-blockers, like metoprolol and propanolol, antagonize the effects of adrenaline on β-receptors in the heart. As a result, they reduce the stimulatory effects on the heart rate (HR) and blood pressure (BP), causing a decrease in the force and rate of contraction. Adrenaline normally stimulates the heart to beat faster and with more force, shortening the ejection time.
In contrast, β-blockers slow down the HR, lengthen the ejection time, and allow the heart to work less strenuously. This action is beneficial in conditions such as hypertension and heart failure. However, one must be cautious of overprescription as it may lead to excessively slowed HR or even bradycardia, potentially causing adverse cardiac events.