ST. LOUIS PARK, Minn. -- Atenolol. A tough heart medication to say - and Dr. Pawan Hari at Park Nicollet in St. Louis Park says - it's getting tough to find.

"Yeah, there's a nationwide shortage of the medication right now and we get phone calls to our physician's office all of the time about the fact that patient's were on the medication but not able to fill the prescriptions at the Pharmacy," said Dr. Hari, a Cardiologist at the Park Nicollet Heart and Vascular Center.

That prescription for Atenolol is used specifically to treat high blood pressure and chest pain. Dr. Hari says - it's popular because it was one of the first beta-blockers on the market and it's inexpensive at only $4 a month.

So, what if you can't fill it up at your Pharmacy?

"We just tell them - first of all - if you're not able to do that, don't panic. Just call your physician's office and consult your physician," said Dr. Hari.

Because there are other inexpensive options, and Dr. Hari says - most people won't even notice any kind of change form Atenolol.

"There's not a huge difference actually. There are several of the newer beta-blockers with similar side effect profiles, if not lesser side effects compared to Atenolol," said Dr. Hari. "Typically a newer medication will take a certain amount of time to build up in your system, so most of these medications will take about 2-3 days to start acting."

Right now, nobody knows what's causing the shortage. Dr. Hari said - none of the drug companies are saying what the missing active ingredient is, which also means, we don't know when this shortage will end.