In connection with capture detection for a heart chamber with backup pacing in a contralateral heart chamber, a cardiac signal of the first heart chamber is sensed following delivery of a pacing pulse. The cardiac response of the first heart chamber to the pacing pulse is classified based on one or more features of the sensed cardiac signal. A backup pacing pulse is delivered to a second heart chamber contralateral to the first heart chamber. For example, the timing of the delivery of the backup pacing pulse may be based on the expected or detected timing of the features used to classify the cardiac pacing response. The backup pace may be delivered within a detection window used for sensing the features indicative of the cardiac pacing response.