What would cause a prolonged P-R interval? What is this called? The velocity of The plood Flow creates a delay in the Pulsc. What happens with a third-degree heart block? Does the heart stop beating? 3. Draw a typical ECG pattern. Label the waves and tell what causes them. Mark the periods of systole and diastole. Mark when S1 (first sound of heart) and S2(second sound of the heart) would occur..