Hi Heilet, and all you warriors.
Eliminate all added sugar in food and drink.
Cut your carbs slowly.

Portion control.
I plate all my food on a 7 inch plate before eating.

Half plate very low carb vegetables.
Quarter plate protein.
Quarter plate high fiber carbs or a serving of diabetes friendly whole fruit.

Walk 10-15 minutes immediately after eating. This redirects blood from digestion to walking muscles. It lowers the glucose spike.

Drop some pounds to bring your BMI down to 18% to 24.9%. The normal range.
Do what you need to do.

And never give up, never surrender, never ever.
You got this.
Have a wonderful day.

To prevent high blood sugar you have to stop putting things in your mouth that jack it up out of range

Simple answer but difficult to put in practice

Alternately it may be time to talk to the Doctor about adding another diabetes drug that deals with "mealtime" blood sugar

The Glucophage works on sugars your body produces itself but is of zero help to what you put in your mouth. If what he is eating is causing the highs then either a dietary change or medication designed to deal with that is the solution

Particularly since he has existing heart condition continued high blood sugar will make that condition worse and possibly deadly, so not something to mess around with too long

Get into the Doctor, express your concerns and get a solid plan

How can he prevent high bloodsugar levels