I weigh about 343 pounds i work out in the gym if i i'm out of breat when i'm in the gy ok i can do cardi 3 30 minutes without feeling out of breat what's wron?

Cardiac Eval: Look, of course I do not know you, but unless you are 9 ft tall, 343 is probably way overweight. The best way to find your answer would be to see a cardiologist and have a good cardiac evaluation, probably including a stress test and echocardiogram. They could then give you a rational program of exercise to help improve your health and/or make other suggestions.