Direct-acting agents are medications that work directly on specific receptors or enzymes in the body to produce a desired effect. They are often used to treat various medical conditions, such as hypertension or heart failure, by targeting the underlying mechanisms of these diseases. These agents can provide rapid relief of symptoms and are typically more effective than indirect-acting agents, which require additional steps to exert their effects. Examples of direct-acting agents include beta-blockers and ACE inhibitors, which help regulate blood pressure and improve heart function.