ABSTRACT : The word kala has been used in many senses in vedic & other ancient literature , Kala Sharira is an important part of Ayurvedic anatomy. Kala was first time described by Sushruta. He has explained kala as a barrier between dhatu and its ashaya Vagbhata has then added embryological development that it is the important physical and functional components of the body. They form a protective coating for the ashayas as well as boundary between the ashayas and dhatus. There are seven kala in the body, in which second kala is Raktadhara kala. Kala sharira (anatomy and physiology of kala) gives us information about the important membranes and layers of the body which take part in many important functions of the body. Acharyas of Ayurveda have described the Anatomy & Physiology of Raktadhara kala in very brief manner.It is explained that Raktadhara kala holds the Raktadhatu (Blood) & present especially in sira (vessels), yakrita (liver) & pleeha (speen) but which structure inside of them is responsible for Raktadhara kala is not clearly mentioned. Hridaya (Heart) is an important organ of blood circulatory system but it is not included as a specific site of Raktadhara kala. So for proper understanding, it is essential to correlate it with the modern science & elaborate in a proper way.