A 
system and method which employs atrial discrimination algorithms to distinguish between different 
atrial arrhythmias occurring in a patient for selecting an optimal pacing therapy corresponding to the type of arrhythmia identified. The invention may be implemented in a 
bradycardia pacemaker or other implantable 
cardiac device. In response to the detection of an 
atrial rate above the atrial tracking rate, discrimination criteria are applied to a detected atrial activity 
signal to distinguish between different types of 
supraventricular tachycardia, such as fast 
atrial flutter and other 
atrial flutter at a relatively slower rate, which may be occurring in the patient. The discrimination criteria may be, for example, rate-based or morphology based. The pacer is controlled to provide pacing therapy to a heart in a manner corresponding to the type of 
supraventricular tachycardia identified. For example, 
antitachycardia pacing may be provided to the heart in response to the detection of a relatively lower rate 
supraventricular tachycardia / other 
atrial flutter, whereas another pacing control, e.g., 
ventricular pacing, such as 
ventricular rate regulation or Rate 
Smoothing, may be applied if a more 
rapid rate supraventricular 
tachycardia / fast atrial 
flutter is identified. The output of an atrial discrimination 
algorithm may be tracked and the trend thereof used to improve therapy timing.