A relatively compact implantable cardiac medical device includes a wireless communications module, which employs a directional antenna and which is adapted to receive input concerning ventricular wall motion. When the cardiac medical device is anchored to a ventricular wall, transmitter elements of the communications modules are only activated for communication during a detected period of reduced ventricular wall motion. The period of reduced ventricular wall motion may be defined as at least one time interval during which an axis of the directional antenna does not rotate out from a baseline orientation by more than 15 degrees. The communication may be conducted with an external programmer-type device, or with another implanted device, for example, located remote from the heart.
