That looks like a PVC and a fully compensatory pause in the middle of a tachycardia (you may be able to assume sinus tach, but it'shard to say where the P waves are coming from based on a single lead). Was this in the middle of exercise, or was the person sick? How old is the person? The underlying rate here is clicking right along at just under 150 bpm.

But, take everything I say with a disclaimer: I am very much an ECG amateur, being an EMR with the local ambulance service whose inner nerd got set off when he saw an ECG machine in action during his training...probably a side effect of being an electrical engineer by day. I've watched a lot of videos and done a lot of electrocardiography and electrophysiology reading (at least for a hobbyist), but I am in no way qualified to do a formal ECG reading.