30r20 70% HRR - 1:47.8 Ave Pace??

So trying to keep up with pre work AM rows (just 30r20 @ 70% HRR - 146) and as I was off worked yesterday - today is my Monday - looked at my last one of these and targeted the first split of it as a start - but emm the HR wouldn't come up - so I dug in a little deeper to push it on - the HR didn't reach 146 for the first time until 20 minutes - no warm up or cool down - but some lovely meters - still tired in the legs but the heart as usual carries me on