Now I personally don't think the heart pain has to do with the horse stance especially for 2 and half minutes. It is a painful practice and I applaud you for doing it since I avoid it personally, but I have known people who practice stances for 30 minutes and an hour as their regular practice.
I think the heart pain could be any kind of health issue and you should see your doctor as see what it might be.
See a doctor. The mabu stance has been done for about 500 years now, so I'm guessing it's you and not the stance. Yeah, 30 minutes to an hour at a time is what a lot of wushu exponents routinely do.
Chest pain can be so many things. How do you know it is your heart and not your stomach? Acid reflux can cause chest pain also. Inflammation can cause pain too. So you see, you are no medical expert and neither are we. Go see a doctor instead of trusting your health to a bunch of underage kids.
Ma bu can cause health problems if you do it wrong or have medical issues to begin with. So make sure you are correctly aligned when sitting in mabu. The key to holding the stance for a long time is to relax into the stance and stay relaxed. It is not done just with strength and you give all indication that you don't include relaxation at all.
I think you're tightening your chest too hard when using the leg muscles. Try to ease up on that and breath in long, breath out short.
Leg exercises don't do much to stress the heart, unless you got a heart condition or a back condition.
Ask your doctor. You may have a specific heart issue that does not affect most people. Mabu may not be causing it, but it could be revealing it.
Again, please consult a doctor about this as soon as possible.
So I perform the mabu stance everyday for 2 and a half minutes before I go to bed. The mabu is harder than the normal horse stance because your thighs are completely parallel to the ground when you are doing it, and your back is straight. Like in the picture above.
I've been doing it for 1 year now and about 4 months ago I started getting these very sharp and chronic heart aches which lasted for a few seconds(I had to push against my chest with my hand when this happened). This happened at various times of the day. An experienced person told me that it could be because of the MABU because the heart is working very hard during the MABU session.
Plus the pain in my legs are almost unbearable when it comes to like 2 minutes in my mabu but I do it anyway. My thigh muscles are well grown because of this exercise and now I can run pretty damn fast because of it... It has its good side but .... My question is, If I do the MABU everyday for 2.5 minutes will it affect my health in anyway? I mean in a bad way..
By the way, I'm 16 and I do a Shaolin Kung Fu