You are describing a symptom called "skip beats". This can be caused by PAC's or Premature Atrial Contractions or PVC's -Premature Ventricular Contractions. You will have to consult with a Cardiologist to figure out which type you have. They will do a resting electrocardiogram-EKG, possibly and echocardiogram
to detect any kind of structural abnormality in the heart, and a treadmill test to see if the skip beats worsen with exercise. Depending on your age and the presence of risk factors ( high cholesterol
, family history, tobacco smoking) the problem could be benign or related to a more serious condition. Some common causes of this type of abnormal rhythm or arrythmia
include stress, caffeine, illicit drugs like cocaine, amphetamines
, crack, cannabis,etc.