Have you had an echocardiogram? Maybe get one, just for reassurance and to make sure there's no serious damage already done.
Magnesium - specifically highly bioavailable forms, chelated or bisglycinate - supplements should help with some stimulant related muscle tension - although I'm not sure offhand if it will make any significant difference to the cardiac effects, I think it may do but please don't take this as gospel.
I did some research on this a while back and dug up the research I could find - here's a link to the thread if you're interested -
https://www.bluelight.org/xf/threads/methods-to-reduce-cardiotoxicity.805255/
The takeaway as far as I could tell is that supplementing selenium is the only thing that really, MAYBE might have some beneficial effect, but this has not been explicitly proven.
Do you have a blood pressure monitor? If not, get one. Educate yourself about what ranges are healthy. Start recording your blood pressure at fixed times in the day and make sure it's healthy when you're sober. When you do cocaine, occasionally record it too - you should expect an increase, but make sure you're not in the danger zone, if you are then you have cause for concern. I know no-one likes to take some of the fun out of a guilty indulgence or whatever, but don't bury your head in the sand - if you're serious about your health, you will keep an eye on this kind of stuff.
Really the best safeguard is to make sure you're in good health generally. You must exercise. You must eat a healthy diet. Eat a high fat, low carb diet, and make sure those fats are healthy fats, there are multiple studies supporting the positive impact of this on heart health. If you want to keep doing cocaine you must cut back in other areas, keep processed sugar to a minimum, don't smoke, if you must smoke, vape, but be aware that even pure nicotine has been linked to increased incidences of cardiac side effects and atherosclerosis.
Cocaine is a disproportionately harmful stimulant with specifically cardiotoxic effects that other stimulants do not share, the ideal would be to switch your cocaine evenings or whatever for another less harmful drug, of which there are many which you would probably enjoy just as much if not more. But if you're hellbent on continuing to use cocaine then please just make every effort to stay healthy otherwise and keep an eye on yourself, monitor your vitals, look after each other, listen to your body and know when enough is enough.
One final thing, if you're not certain of the quality and want to ensure you're not also imbibing other cuts, some of them stimulating in themselves like ephedrine or something, lookup how to do an acetone wash to purify your cocaine and make sure that what you're taking is, truly, just cocaine. Cocaine itself is harmful however, so doing this will not massively reduce the cardiac risk which is why I mention it last - but it's something to consider if you truly want to cover all your bases.