Is it possible that cardioversion correct an abnormal heart rythm due to prolonged pr interval?

In general no: If the heart rhythm problem is any type of heart block (first degree av block, second degree av block, or complete heart block), cardioversion won't help. Having said that, certain types of cardiac rhythm problem (such as atrioventricular nodal reentrant tachycardia (avnrt)) can in rare cases look like a fast heart rhythm with a long pr interval. These a cardioversion could correct.