ACE inhibitors are a class of medications that block the angiotensin-converting enzyme, leading to decreased production of angiotensin II, a potent vasoconstrictor. This results in vasodilation, reduced blood pressure, and decreased workload on the heart, making them essential in managing hypertension and heart failure. A key example is enalapril, and a notable complication is the risk of hyperkalaemia due to decreased aldosterone secretion.