My girlfriend is a 52 y.o. female. She said she didn’t feel good and her left side was kind of tingly. I took her pulse, it was 72 bpm, but every 20 to 24 beats it seemed to miss one. Her temperature is normal. What could it be?

A left sided tingling can be of numerous causes. The two most causes to rule out in a woman at the age of 52 are neurologic and cardiac in nature.

It terms of neurologic causes, your girlfriends symptoms are suspicious for either stroke or a transient ischemic attack (TIA). It is important to recognize the warning signs of a stroke which include:
Sudden onset numbness or weakness of the face, or extremity – especially if its only limited to one side of the body
Sudden onset visual disturbance one or both eyes
Sudden onset of confusion, difficulty speaking or understanding
Sudden onset of difficulty walking or loss of balance/coordination.

Cardiac causes include arrythmias, atrial fibrillation, or even heart attacks (myocardial infarctions) can present with similar symptoms as you are describing.

Your girlfriends symptoms are serious and warrant prompt medical attention. She should be evaluated immediately by either her primary care physician or a local emergency room. Tests such as a 12-lead EKG and noncontrast Head CT scan should be standard in the workup of her condition.