If you are using a Suunto heartrate belt with a PM4, you need to press More Options / Connect Suunto HR Monitor to register your Suunto heartrate belt before starting RowPro.
If you forget, you need to close RowPro, register your Suunto heartrate belt on the PM4, and then restart RowPro.
Page url: http://www.digitalrowing.com/support/help/index.html?important___using_a_suunto_hr_.htm