My heart beats three times the skips a beat and beats another three times then skips again. On the first beat after the skip it pumps twice as hard?
You're good! You're a very good observer! you describe a rhythm called "quadrigeminy." every 4th beat is premature. Because the heart doesn't like irregularity, it pauses a few extra milliseconds to jump back into the original rhythm. During that brief pause, the chambers fill more and prouduce a more powerful next beat called "post-extrasystolic potentiation." none of this is dangerous.
See your doctor. As soon as possible, to find the cause and to treat you. You r irregular heart beat , most likely PVC s , ( pre mature ventricular contractions ) if untreated may lead to serious cardiac arrhythmia, for get about heart working twice as hard. Slow heart rate of athletes , allows ventricle to fill more blood, to give more ejection volume (starling principle ).