A medical device comprising: a cardiac electrical signal sensing circuit configured to: receive a first cardiac electrical signal; sense cardiac events from the first cardiac electrical signal; a control circuit configured to: determine time intervals between consecutive cardiac events sensed from the first cardiac electrical signal; detect a plurality of tachyarrhythmia intervals from the determined time intervals, each of the plurality of tachyarrhythmia intervals being less than a tachyarrhythmia detection interval threshold; increase a value of a tachyarrhythmia interval count in response to detecting each of the plurality of tachyarrhythmia intervals; detect a normal sinus rhythm interval from the determined time intervals, the normal sinus rhythm interval being greater than a normal sinus rhythm interval threshold; determine that a first reset threshold number of normal sinus rhythm intervals are detected; decrease the value of the tachyarrhythmia interval count in response to the first reset threshold number of normal sinus rhythm intervals being detected; and after decreasing the value of the tachyarrhythmia interval count, determine that the tachyarrhythmia interval count subsequently reaches a tachyarrhythmia detection threshold; detect a tachyarrhythmia in response to the value of the tachyarrhythmia interval count reaching the tachyarrhythmia detection threshold; and a therapy delivery circuit configured to deliver a tachyarrhythmia therapy in response to the control circuit detecting the tachyarrhythmia. a cardiac electrical signal sensing circuit configured to: receive a first cardiac electrical signal; sense cardiac events from the first cardiac electrical signal; receive a first cardiac electrical signal; sense cardiac events from the first cardiac electrical signal; a control circuit configured to: determine time intervals between consecutive cardiac events sensed from the first cardiac electrical signal; detect a plurality of tachyarrhythmia intervals from the determined time intervals, each of the plurality of tachyarrhythmia intervals being less than a tachyarrhythmia detection interval threshold; increase a value of a tachyarrhythmia interval count in response to detecting each of the plurality of tachyarrhythmia intervals; detect a normal sinus rhythm interval from the determined time intervals, the normal sinus rhythm interval being greater than a normal sinus rhythm interval threshold; determine that a first reset threshold number of normal sinus rhythm intervals are detected; decrease the value of the tachyarrhythmia interval count in response to the first reset threshold number of normal sinus rhythm intervals being detected; and after decreasing the value of the tachyarrhythmia interval count, determine that the tachyarrhythmia interval count subsequently reaches a tachyarrhythmia detection threshold; detect a tachyarrhythmia in response to the value of the tachyarrhythmia interval count reaching the tachyarrhythmia detection threshold; and a therapy delivery circuit configured to deliver a tachyarrhythmia therapy in response to the control circuit detecting the tachyarrhythmia. determine time intervals between consecutive cardiac events sensed from the first cardiac electrical signal; detect a plurality of tachyarrhythmia intervals from the determined time intervals, each of the plurality of tachyarrhythmia intervals being less than a tachyarrhythmia detection interval threshold; increase a value of a tachyarrhythmia interval count in response to detecting each of the plurality of tachyarrhythmia intervals; detect a normal sinus rhythm interval from the determined time intervals, the normal sinus rhythm interval being greater than a normal sinus rhythm interval threshold; determine that a first reset threshold number of normal sinus rhythm intervals are detected; decrease the value of the tachyarrhythmia interval count in response to the first reset threshold number of normal sinus rhythm intervals being detected; and after decreasing the value of the tachyarrhythmia interval count, determine that the tachyarrhythmia interval count subsequently reaches a tachyarrhythmia detection threshold; detect a tachyarrhythmia in response to the value of the tachyarrhythmia interval count reaching the tachyarrhythmia detection threshold; and