Which of the following beta blockers has intrinsic sympathomimetic activity?

Acebutolol is the correct answer because it is a unique beta blocker that possesses intrinsic sympathomimetic activity (ISA). This means that while it blocks beta-adrenergic receptors, it also stimulates them to a certain degree, mimicking the effects of adrenaline. This characteristic helps reduce heart rate and blood pressure without causing a complete blockade of the sympathetic nervous system's effects, which can be beneficial in maintaining some heart activity during treatment.

In contrast, the other options listed do not exhibit intrinsic sympathomimetic activity. Metoprolol and bisoprolol are both selective beta-1 blockers that primarily reduce heart rate and myocardial contractility without stimulating the receptors they block. Carvedilol, although it has additional properties as a non-selective beta blocker and an alpha-1 blocker, does not exhibit ISA. Thus, understanding the unique properties of acebutolol is essential for recognizing its application in clinical settings, particularly where a moderate sympathomimetic effect may be advantageous.