Union on timechart

OmriPinsker 

If you need a different date range for each Table, then this maybe better: Go to Log Analytics and run query

union  
    (
    Heartbeat
        // go back two days and get a bin for each day
        | where TimeGenerated > startofday(ago(2d))
        | summarize Count=count() by bin_at(TimeGenerated, 1d, now())
        | order by TimeGenerated
        | project Value = iff(isnull(Count), 0 , Count), Time = TimeGenerated, Legend = "Table1: Heartbeat" 
    ),
    (
    Perf
        // go back seven days and get a bin for each day
        | where TimeGenerated > startofday(ago(7d))
        | summarize Count=count() by bin_at(TimeGenerated, 1d, now())
        | order by TimeGenerated
        // perf is a high count so added a /1000 to reduce the scale - please remove
        | project Value = iff(isnull(Count), 0 , Count / 1000), Time = TimeGenerated, Legend = "Table2: Perf" 
    )
| render timechart

Count and max(Count) would have been the same in the examples given, so I removed that line.