Lily of the Valley (Convallaria majalis) has a long history of use in European herbal medicine for the treatment of heart conditions, particularly "heart weakness" (a term historically referring to symptoms of heart failure). Unlike some folk medicines, its use is not solely traditional; there is a scientific basis rooted in its phytochemistry. The plant contains cardiac glycosides, primarily convallatoxin, which have a mechanism of action similar to digoxin (from foxglove). These compounds increase the force of heart muscle contractions and can help in cases of congestive heart failure or arrhythmias. In the late 19th and early 20th centuries, Lily of the Valley extracts were clinically used as alternatives to digitalis, especially in Europe, due to their reportedly milder side effect profile.

However, compared to digoxin, Lily of the Valley preparations are less potent and have a narrower therapeutic window, making dosing challenging. Modern clinical use is rare, as standardized dosing and safety data are lacking. Most contemporary support comes from pharmacological studies confirming the presence and action of cardiac glycosides, but robust randomized clinical trials in humans are scarce. Thus, while scientific validation exists at the mechanistic and historical clinical use levels, high-quality evidence from modern research is limited, justifying a moderate evidence rating.