My mum is 48 she has some tightness and pressure in her chest and left arm..she has gerd..she thinks its coz of this..m worried. is it something else?

Possible: Yes, this could be something more serious. While GERD, pneumonia, rib pain, chest wall sprain can all feel the same, so can cardiac chest pain. Even if she did not have heart disease before, the next time may be different. It is always best to get this evaluated by her doctor to make sure, especially if it is recurrent. It is better to be overly vigilant than miss the one time it is critical.