This ECG is challenging. The rhythm starts as normal sinus rhythm ... This is not obvious on the 12-lead ECG tracing, although the heart rate during the tachycardia is almost exactly 150 beats ...

This ECG has a narrow QRS complex initally, then a fast heart rate, regular rhythm and no identifiable P wave activity which suddenly turns to a wide complex in a left bundle branch block pattern.

Irregular heart rhythm -- arrhythmia -- is when your heart doesn't keep up a good beat. Learn what it means here. You may not know what a heart valve is -- until it stops working right.