According to the Merck Manuals Online Library, the heart beats at around 60 to 100 beats per minute in adults at rest. The rate at which the heart beats can be affected by drugs, hormones, or a trigger from the nervous system. For example, it is common knowledge that fear causes the heart to beat faster. Many different symptoms can be caused by the physical effects of a changing heart rate.
Palpitation
The Merck Manuals Online Library dispels the myth that palpitations are always a sign of trouble. It asserts that many people are sometimes aware of their normal heart beats, especially when lying on the left side. However, the Heart Rhythm Society flags palpitation as a sign of potential serious trouble necessitating a doctor's visit. The Heart Rhythm Association describes palpitation as the feeling of skipping a beat. Many people describe this sensation as pounding or fluttering. Palpitation in most instances is due to arrhythmia or an abnormal rhythm of the heart.
Slow Heart Rate
When the heart beats below 60 beats per minute, the patient is said to have bradycardia. This bradycardia may cause no ill effects; or, as pointed out by the Heart Rhythm Society, could be very devastating to the body due to the reduction in the amount of blood pumped by the heart in a given minute. This may manifest as shortness of breath, dizziness, lightheadedness, weakness, or fainting. It is important to note that the Heart Rhythm Society mentions that in some people, like professional athletes, the resting heart rate may be below 60 beats per minutes with no symptoms or ill-effects.
Rapid Heart Rate
As noted by the Heart Rhythm Society, rapid heart rate, or tachycardia, is usually defined as heart rate above 100 beats per minute. When the heart beats too fast, the ventricles do not have enough time to fill with blood. Consequently, the amount of blood pumped into the arteries is markedly reduced and the blood pressure may drop. Fainting can occur if the blood going to the brain is not adequate for its oxygenation. The Heart Rhythm Society points out that one of the arrhythmias causing rapid heart rate is the dreaded ventricular fibrillation. Ventricular fibrillation is the number one cause of sudden death due to a cardiac cause.
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