Changes in P-R interval immediately before, during, and after acute myocardial infarction.

A 48 years old male developed acute cardiac pain manifested by prolonged P-R interval as the only electrocardiographic sign. Subsequently the electrocardiogram evolved an acute myocardial infarction with a normal P-R interval. Immediately therafter prolonged P-R interval reappeared to become established even after digitalis was long discontinued.