A Wenckebach block is a type of conduction disturbance of electrical signals from the sinus node of the heart to the ventricles. It is clinically observed as an intermittently missed beat at regualr intervals. EKG shows a progressive increase in the duration of the P-R interval in successive cycles until an atrial impulse fails to activate the ventricles. Dropping of QRS cmplex usually occurs when the P-R interval reaches 0.34 seconds or more. The Wenckebach block is a second-degree block subclassified as Mobitz type I.