Some arrhythmias don’t cause any symptoms. Others announce themselves quite clearly, perhaps with the distinct feeling that the heart is racing. Still other arrhythmias cause symptoms that aren’t obviously heart-related, such as lightheadedness or dizziness. Most adults will, at some point, experience fleeting, and harmless heart rhythm changes. Certain arrhythmias, especially those that last long enough to impact heart function, can be serious or even fatal.

Palpitation or a Skipped Beat
Although it may seem as if the heart missed a beat, really the heart has a premature heartbeat, almost an extra beat happening too soon, which may result in a pause – the "skipped beat." [more]

Fluttering
A fluttering sensation is usually due to a series of "skipped beats" that occur in quick succession. [more]

Slow Heartbeat – Bradycardias [more]
If the heartbeat is too slow, usually considered a rate below 60 beats a minute, not enough oxygen-rich blood flows through the body. So, it makes sense that the symptoms of a slow heartbeat are:

• Fatigue
• Dizziness
• Lightheadedness
• Fainting or near fainting

Rapid Heartbeat – Tachycardias [more]
When the heart beats too quickly, usually considered a rate above 100 beats a minute, the lower chambers, or ventricles, do not have enough time to fill with blood, so they cannot effectively pump blood to the rest of the body. When this happens, some people experience:

• Skipping a beat
• Beating out of rhythm
• Palpitations
• Rapid heart action
• Shortness of breath
• Chest pain
• Dizziness
• Lightheadedness
• Fainting or near fainting
• Chaotic, quivering or irregular rhythm
  

Suddenly rapid, irregular and chaotic heartbeats may be a sign of the most dangerous arrhythmia, ventricular fibrillation. It is the number one cause of sudden cardiac death. Within seconds, an individual loses consciousness and, without immediate emergency treatment, will die within minutes.

Almost Fainting – Presyncope
Sometimes people experience symptoms before they faint. Presyncope can be a sign of a heart rhythm disorder and should be evaluated carefully.

• Dizziness, lightheadedness or vertigo
• Blurred or narrowed (tunnel) vision
• Sweating
• Nausea and/or vomiting
• Stomachache/abdominal discomfort
• Heart palpitations
• Headache
• Confusion and/or difficulty
• speaking clearly or coherently

Fainting - Syncope [more]
Fainting related to a heart rhythm disorder is more likely to happen suddenly and without warning than fainting related to other causes, such as dehydration or low blood sugar. Any sudden lose of consciousness should be evaluated by a physician.
In some cases, fainting is the only warning sign of an arrhythmia that could cause sudden cardiac death.