In the latest date, medical body area networks (MBANs) are emerging as a new technology for diagnosis the human body. MBANs in the health care fields are based on short-range and low-power (e.g. ubiquitous computing) among small-sized devices, and have been used by means of medical services. In this paper, we proposed an emergency message transmission protocol using carrier sense multiple access/time division multiple access in MBANs. This scheme focuses on dependability and power-efficiency. In order to increase the reliability of the transmission, this scheme modified a MCTA slot of IEEE 802.15.3 standard to a SR-MCTA slot. SR-MCTA slot is assigned by MBAN coordinator according to requesting terminal nodes. The method, having the priority of transmission, occurs a collision packet randomly. Results from this proposed solution revel that reservation-based TDMA medical body area network(MBAN) protocol for transmitting emergency message was improved in terms of transmission delay.