Heartwood, typically referring to the inner, non-living wood of a tree, is a term broadly used for the central wood of various medicinal trees such as Pterocarpus santalinus (Red Sandalwood) or Acacia catechu (Catechu). In Ayurvedic and other traditional systems of medicine, certain "heartwoods" have been employed as remedies for urinary tract issues, including kidney stones (urolithiasis). For example, Pterocarpus santalinus is cited in Ayurvedic texts for its purported diuretic and anti-urolithiatic properties, and decoctions or powders of the heartwood are used in traditional formulations aimed at supporting kidney and urinary health.

However, the scientific evidence supporting the use of heartwood (of any specific species) for kidney stones is limited and primarily based on in vitro or animal studies. There are a few preliminary studies suggesting that extracts from certain heartwoods, such as Pterocarpus marsupium or Acacia catechu, may reduce stone formation or promote diuresis in animal models, but robust clinical trials in humans are lacking. Therefore, while there is a traditional basis for the use of heartwood in the support or treatment of kidney stones, scientific validation remains minimal. The evidence rating of 2 reflects this reliance on traditional knowledge and low to moderate preclinical support, but insufficient human data.