Explain Extrasystole and Compensatory Pause

During the relaxation period, cardiac muscle is in the relative refractory period i.e. sleeping but only just. If a sufficiently strong electrical stimulus is applied during this period, it leads to a contractile response. Since this contraction appears earlier than the normally expected contraction, it may be considered an 'extra' contraction. Hence, it is called extrasystole. The next natural impulse then arrives during the refractory period corresponding to the extrasystole. Hence, the natural impulse is ineffective and a normally expected contraction is missed. As they say, "I missed a beat". The pause in cardiac activity is called compensatory pause. In real life, if we drink too much coffee, the heart fires leading to premature contraction of the ventricles and extrasystole may be produced.