A system for artificial stimulation of the heart of a subject, the system comprising: a controller assembly (8, 908) comprising a receiver for receiving signal data, a processor for processing received signal data, and a transmitter for transmitting signal data; a single sensing stent (4, 702, 802, 904, 1002, 1020, 1040, 1060, 1080) configured to be located in the proximal region of the coronary sinus at or adjacent the ostium of the coronary sinus of the subject, the sensing stent (4, 702, 802, 904, 1002, 1020, 1040, 1060, 1080) comprising a sensing electrode assembly for sensing atrial and ventricular signals from the heart of the subject and a transmitting assembly for transmitting signal data to the receiver of the controller assembly, the sensing stent comprising one or more openings or bores therethrough permitting the passage of blood through or past the sensing stent; wherein the sensing stent (4, 702, 802, 904, 1002, 1020, 1040, 1060, 1080) is not capable of providing electrical stimulation to the heart of the subject; a stimulation stent (10, 12, 14, 16, 18, 102, 202, 302, 402, 502, 602, 910, 912, 914, 916, 918) configured to be located in a vein of the subject distal of the sensing stent, the stimulation stent (10, 12, 14, 16, 18, 102, 202, 302, 402, 502, 602, 910, 912, 914, 916, 918) comprising a receiver for receiving signal data from the transmitter of the controller assembly (8, 908) and an electrode assembly for providing a stimulating electrical signal to the heart of the subject in response to the data received; and a defibrillator assembly for providing stimulation to the heart sufficient to defibrillate the heart in response to a signal received from the controller assembly (8, 908). a controller assembly (8, 908) comprising a receiver for receiving signal data, a processor for processing received signal data, and a transmitter for transmitting signal data; a single sensing stent (4, 702, 802, 904, 1002, 1020, 1040, 1060, 1080) configured to be located in the proximal region of the coronary sinus at or adjacent the ostium of the coronary sinus of the subject, the sensing stent (4, 702, 802, 904, 1002, 1020, 1040, 1060, 1080) comprising a sensing electrode assembly for sensing atrial and ventricular signals from the heart of the subject and a transmitting assembly for transmitting signal data to the receiver of the controller assembly, the sensing stent comprising one or more openings or bores therethrough permitting the passage of blood through or past the sensing stent; wherein the sensing stent (4, 702, 802, 904, 1002, 1020, 1040, 1060, 1080) is not capable of providing electrical stimulation to the heart of the subject; a stimulation stent (10, 12, 14, 16, 18, 102, 202, 302, 402, 502, 602, 910, 912, 914, 916, 918) configured to be located in a vein of the subject distal of the sensing stent, the stimulation stent (10, 12, 14, 16, 18, 102, 202, 302, 402, 502, 602, 910, 912, 914, 916, 918) comprising a receiver for receiving signal data from the transmitter of the controller assembly (8, 908) and an electrode assembly for providing a stimulating electrical signal to the heart of the subject in response to the data received; and a defibrillator assembly for providing stimulation to the heart sufficient to defibrillate the heart in response to a signal received from the controller assembly (8, 908).