I took an ECG after a finishing a cycle ride and mowing the lawn.
I had never seen anything like this before. It settled down straight after and was fine for the next few hours. I assume that there must have been some interference for the baseline to move so much, but even so the trace was a bit worrying. It was scorching today, but I wasn’t dehydrated and the last two bike rides were gentle with an average HR of 138 with only one or two short bursts in the low 160s.