The Heartbeat event belongs to Software events category (category 400000000). When you configure alerting that uses SMTP channel for Software Events, the SMTP recipients would receive daily email notification for heartbeat event (event ID 400050004)
You can list all the event type in the Software category using the following command:
# isi event types list --category=400000000
Now, if you want to exclude the HeartBeat event (400050004) from Alerting, you will have to remove the entire Software category, and explicitly specify the other events you want to receive.
# isi event alerts modify <alertname> --add-eventgroup= "400020001,400020002,400030001,400030002,400040012,400040020,400040021,400050001,400050002,400050003,400060004,400070004,400070005,400070006,400070007,400080001,400090001,400090002,400090003,400090004,400100001,400100002,400100003,400100004,400100005,400100011,400110001,400120001,400130001,400130002,400140001,400140002,400150001,400150002,400150003,400150004,400150005,400160001,400210001,400210002"
I hope this helps.
Karim.