Background: Parthadyarishta (PRTm) is an Ayurvedic preparation used as a traditional medicine to treat heart disease. This research was designed to study the thyroid hormone profile after chronic administration of this drug. Methods: Twenty healthy Sprague-Dawley male rats (90-110 g) were randomly divided into a control group and an experimental group. The experimental group was assigned to receive the drug at a dose of 40 ml/kg of body weight orally. After 28 days of treatment, blood samples were collected to carry out biochemical tests to determine the thyroid hormone safety profile. Serum circulating levels of total thyroxine (tT4), total triiodothyronine (tT3), free thyroxine (fT4), free triiodothyronine (fT3), thyroid stimulating hormone (TSH) were measured by Chemiluminescent Microparticle Immunoassay (CMIA) method. Results: This study showed statistically significant (p=0.008) [21.93%] decrease in tT3 level and statistically significant (p=0.047) [10.73%] increase in fT3 level in the rats. Also, statistically insignificant decrease in tT4 level and increase in fT4 level were observed. There is a [49.96 %] decrease in TSH level (p=0.371). The results suggested that Parthadyarishta have exerted an opposite effect on both the total and free form of T3 by increasing the free form (fT3) though causing decrease in the total form (tT3). Conclusions: As Parthadyarishta has significant impact on thyroid hormone levels so it is recommended to use it cautiously for chronic use specially in cardiac patients. Further studies are needed to determine the toxicological profile of Parthadyarishta and its effect on cardiovascular system through interference in thyroid function.