a contraction of the heart caused by a stimulus or impulse somewhere in the heart other than in the sinoatrial node, its natural pacemaker
A form of arrhythmia often referred to as "an extra heartbeat".
An ectopic beat, occurring before the next dominant beat, that depends on and couples with the preceding beat; contraction of the heart that occurs prematurely and interrupts the normal cardiac cycle.
Related Topic"An ectopic or asynchronous beat from any source in the heart..."
A premature contraction of the heart, in most cases harmless.