A cardiac contractility modulating (CCM) device (30) includes an anti-arrhythmic therapy unit (38) for detecting a cardiac arrhythmia in a heart (2) of a patient based on processing electrical signals related to cardiac activity sensed at the heart, and for delivering anti-arrhythmic therapy to the heart. The device includes a cardiac contractility modulating (CCM) unit (40) capable of delivering cardiac contractility modulating (CCM) signals to the heart for modulating the contractility of a portion of the heart. The device may provide to the anti-arrhythmic therapy unit control signals associated with the delivery of the CCM signals to the heart. The control signals may be used to prevent interference of the CCM signals with the detecting of the cardiac arrhythmia. The device (30) includes a power source. The device may be an implantable device or a non-implantable device. The device may also include a pacing unit.