The heart must maintain a steady rhythm in order to pump properly. Excessively slow heart rhythms cause the cardiac output to be insufficient, and this can cause symptoms of fatigue, weakness, lightheadedness, fainting, shortness of breath, and fluid accumulation (i.e. "congestive heart failure"). On the other hand, if the heart beats too quickly it doesn't get enough time in between beats to fill up with blood. As a result, only a small amount of blood gets squirted out with each beat, and the cardiac output drops significantly. In order to understand this, imagine trying to put out a large fire with a shot glass. You can fill this tiny glass very quickly and splash the fire with lots of little drops, but it's much more efficient to fill a large bucket and douse that fire with only a couple of trips to the faucet. Rapid heart rhythms decrease the efficiency of the heart's pumping action, and this can cause the same symptoms as a slow heart rhythm, namely, weakness, shortness of breath, and fainting. In addition, rapid heart rhythms can cause a symptom known as "palpitations."
The word "palpitation" refers to any abnormal or inappropriate feeling in the chest caused by the heart's beating. It's a generic term, and people can even feel palpitations when their heart is beating normally. Some palpitations can feel like a fluttering, a racing, or a pounding in the chest. Others may feel like a heavy or hollow feeling in the chest, or a feeling of a "skipped" or "missed" beat. For some people they can even be perceived as painful. Sometimes palpitations make you feel like you can't catch your breath. Palpitations can be brief only a fraction of a second, like when the heart "skips a beat." Then again, palpitations can last for several minutes or even hours. Sometimes, brief flutter (skipped beat) type palpitations may occur over and over every few seconds. This can cause an irregular pulse that can last for hours and can be very annoying.
You are probably wondering where all these abnormal rhythms come from and why the heart sometimes beats too fast or too slow. Arrhythmias result from the electrical signal of the heart getting fouled up by a "wiring" problem. Sometimes the signal gets blocked by a "loose connection" and the heart doesn't beat when it is supposed to (because the muscle is not getting the signal). This can cause slow heart rhythms. Sometimes there is a "short circuit" in the wiring which causes the electrical signal to take an abnormal route or to get stuck traveling around and around in a circular pathway. This problem can force the heart to beat rapidly. Sometimes, an abnormal signal will arise from somewhere in the heart and cause the electrical system of the heart to fire prematurely. This is what causes a premature beat. There are many different kinds of rhythm problems caused by many different electrical disturbances. Some cause fast beats and some cause slow ones. Each one of these problems may require different treatment, and some may not require treatment at all. One medication may be good for one kind of rhythm problem and bad for another. Therefore, it is important for your doctor to determine the exact type of rhythm problem that you may have.