If you have travel insurance then you must tell the insurance company that you are being treated for this. It is probably a condition of your policy and if you don't tell them then they won't pay up if you make a claim (for anything even if it's nothing to do with your arteries).

If you don't have travel insurance that covers medical and re-patriation then you should get it. It's a small price to pay for peace of mind, especially if you're travelling outside of the EU (like Turkey), where medical facilities are unknown and can be expensive.

You should also get your doctor to provide an assurance that it is safe for you to fly. Send this to the insurance company. It's not normally a problem for cardio-vascular issues. Aeroplane cabin pressures are set to typically 10,000 feet. That is quite safe for travel but it's enough to cause your ears to become painful as you descend.
Your biggest risk is cramp so to prevent this (and deep-vein-thrombosis) you should wiggle your feet and ankles a lot during the flight, and take a trip of two to the bog (for the walk).

It is not normally necessary to tell the airline about your medical conditions unless you need special arrangements on the plane.

You should carry your doctor's letter and repeat-prescription note with you if you have the drugs on your person or in your baggage. This is because you may have to show it to airport security in the UK and to the Turkish authorites. They can be very severe if they think that you are brining in illegal drugs.

If you are unfortunate enough to be stopped by some Turkish "jobsworth" and you don't have the evidence that the pills are for you it could take several days (oh yes) before they let you out of the police station while YOU prove that they're your own medicine.