The ALERT_PULSE structure is used in the ALERT_MESSAGE structure message, as specified in section 2.2.6.6. 

 struct
 {
   ULONG cbHeaderLength;
   ULONG Reason;
} ALERT_PULSE; 

cbHeaderLength: A ULONG that contains the header length of this message.  

Reason: A ULONG that contains the reason code for the heartbeat message ALERT_VERIFY_NO_KEY, as specified in section 2.2.3.