Coming as little surprise, herbal remedies may interact with cardiac medicines. The WebMD article draws needed attention to an area that is not often mentioned in the promotions of supplement manufacturers.

Some specific examples they cited included:

• St. John's wort, which is typically used to treat depression, anxiety, and sleep problems, has been shown in some studies to decrease the effectiveness of the arrhythmia drug digoxin, as well as blood-pressure-lowering medications and cholesterol-regulating statins. 
• The herbal remedies alfalfa, dong quai, bilberry, fenugreek, garlic, ginger, and ginkgo biloba were all identified by the researchers as increasing bleeding risk when combined with the widely prescribed anti-clotting drug Coumadin (warfarin). Ginseng and green tea were identified as decreasing Coumadin's effects. 
• The banned herbal product ephedra (ma-huang) has been linked to stroke, heart attack, seizures, and death from cardiac arrhythmia in otherwise healthy adults who used the product to boost energy or lose weight.

These are not new examples, and really aren't enough to say that all herbals are bad, but the message is that there is a potential for interactions of which we should be more aware.

We know St. John's wort has a lot of drug interactions, as does coumadin, but doctors should be screening their patients on these, especially coumadin.  I think we as a profession could be spending more time discussing the special diet coumadin users are supposed to eat, as well.

A lot of herbals' goal is an "antioxidant" effect, and I am still waiting for the explanation about what benefits that effect produces.  To me, that lack of efficacy is the reason to avoid most supplements, though to many, that is not a barrier!

Probably we are preaching to the choir here--if you are reading a medical blog, you probably already have a rationalistic approach to medical treatments. 

UPDATE: Here's some info from FDA about dietary supplements, though no specific information on interactions with conventional medicines.