Bradycardia is a condition in which the heart beats too slowly. A healthy heart beats 60 to 100 times per minute, pumping about 75 gallons of blood every hour. With bradycardia, the heart beats fewer than 60 times per minute. At that rate, your body doesn't receive enough oxygen-rich blood to fuel exercise or even just normal activity. As a result, you might feel dizzy, tired, short of breath, or have fainting spells.