A cardiac rhythm management system recognizes patterns of interval durations, distinguishing between events in different heart chambers even though signals associated with those different heart chambers are processed using a commonly shared sensing circuit. A therapy delivery algorithm ignores intervals between cardiac events occurring in different heart chambers when determining a cardiac rate upon which the delivery of therapy is based. This reduces the risk of inappropriate delivery of therapy to the patient. Delayed conduction left ventricular beats are not erroneously recognized as a subsequent right ventricular beat, preventing such short intervals from inappropriately triggering a defibrillation countershock.