Rehmannia (Rehmannia glutinosa) is a prominent herb in Traditional Chinese Medicine (TCM), where it is used to tonify the blood and yin. In classical TCM formulations, such as "Sheng Mai San" and "Liu Wei Di Huang Wan," rehmannia is frequently included to nourish the kidneys, liver, and heart, particularly in cases of "heart yin deficiency" or "heart weakness"—a syndrome characterized by symptoms like palpitations, insomnia, and anxiety. The rationale is largely based on TCM theory, where rehmannia is believed to replenish vital essence and fluids, indirectly supporting heart function.

While there is limited modern scientific evidence directly linking rehmannia to improvements in heart function or treatment of heart failure, some animal studies suggest it may have antioxidant and anti-inflammatory properties, which could theoretically benefit cardiovascular health. However, these findings are preliminary and not specific to "heart weakness" as defined in either Western or Eastern medicine. No high-quality clinical trials have validated its effectiveness for heart weakness or related conditions in humans.

In summary, the use of rehmannia for heart weakness is primarily justified by traditional use in TCM, with little scientific validation at present. Evidence supporting its efficacy for this specific indication is weak and should be interpreted with caution.