Heartbeat required for Microsoft Cluster?

Heartbeat(s) is a Microsoft Cluster requirement, not NetBackup. You should have a list physical requirements from Microsoft before MS Cluster is installed and configured. MS Cluster must be installed and configured before NetBackup is installed as clustered master server.

Thanks Marrianne...

I just found an netbackup guide (Symantec NetBackup in Highly Available Environments Administrator's Guide)  where says "multiple heartbeat connections must exist between the clusters" configure a heartbeat, so I´m a little confused here. I need a document, guide o something where I can find a excact answer about "heartbeat". 

You will find that in Microsoft documentation. The NBU doc is merely mentioning the basic requirement of all clustering products.