Irregular heartbeat. Conceptual computer artwork of a blurred heart and an electrocardiogram (ECG) trace (bottom). The heart is a muscle that pumps blood around the body. The ECG trace shows an extrasystole (irregular) heartbeat, with three ventricular (high) peaks interrupting the usual pattern of one ventricular peak and one atrial (lower) peak. Extrasystole is most often sporadic and harmless, but may indicate an underlying heart condition.