System and techniques for distributed monitoring of cardiac activity include selective T wave filtering. In general, in one implementation, a distributed cardiac activity monitoring system includes a monitoring apparatus, with a selectively activated T wave filter, and a monitoring station. The monitoring apparatus can include a communications interface, a real-time QRS detector, a T wave filter, and a selector that activates the T wave filter to preprocess a cardiac signal provided to the real-time QRS detector in response to a message. The monitoring station can communicatively couple with the monitoring apparatus, over a communications channel, via the communications interface and can transmit the message to the monitoring apparatus to activate the T wave filter based at least in part upon a predetermined criteria (e.g., abnormal T waves for an individual, as identified by a system operator).