A semi-automatic atrial defibrillation system monitors activity of a heart, detects atrial fibrillation (AF), and cardioverts detected AF. The system includes an implantable atrial defibrillator capable of communicating with an external portable device that can further communicate with a remote service centre. The implantable atrial defibrillator is capable of detecting AF, automatically sending warning signal and diagnostic data to an external portable device after detection of AF, receiving commands from the external portable device, and cardioverting AF. The external portable device is capable of sending commands to the implantable atrial defibrillator, receiving data from the implantable atrial defibrillator, providing patient discernable warning signal and brief diagnostic information after detection of AF, and transmitting diagnostic information to the remote service centre. The external portable device is operable by the patient, who may self-control the delivery of atrial cardioversion therapy after receiving the AF warning message, or may contact the remote service centre for physicians advice before taking any action.
