Final answer:
The herb associated with high blood pressure, irregular heartbeat, and heart attack is ephedra due to its ephedrine content, which is similar to amphetamines and can be dangerous.
Step-by-step explanation:
Herbs Associated with Health Risks
The herb associated with the risks of high blood pressure, irregular heartbeat, and heart attack is ephedra. Ephedra, also known as ma huang, is a source of the compound ephedrine. In medicine, ephedrine is used as a decongestant due to its potent effects. However, because ephedrine is chemically similar to amphetamines, it can have serious side effects including high blood pressure, irregular heartbeat, and heart attack. The use of ephedrine is now restricted due to these risks, and it is available only in prescription drugs.
The other herbs listed have different profiles of action and associated risks. For instance, Ginger is commonly used to help digestion and alleviate nausea, St. John's wort is often used for depression but can interact with various medications, and Ginkgo biloba is taken to improve memory, though it too can have interactions with other drugs.