My cholesterol is 300 having breathing issues mostly after eating with mild chest pressure could it indicate heart attack is coming ?

Not necessarily but: Cholesterol IS moderately elevated which places you in a higher risk category for atherosclerosis. But, being a 30 yo woman places you in a lower risk category. In sum, can’t tell. If chest pressure started recently, safest to present to ER tonight just to make sure. If this has been going on for weeks/months, see your doctor ASAP

Cholesterol: You did not indicate if this is total cholesterol or LDL. Lipid profile must be done fasting .if this reading is non fasting then you need a repeat while fasting . Also LDL is the bad cholesterol and goal is to have it less than 100. Do you have any risk factors like diabetes? If you are experiencing chest pressure go to ER or see a cardiologist ASAP.