28/f. Dull ache in left arm starting from elbow to wrist sometimes in upper arm. Dull ache in left thigh also. Could this be heart related?

Probably not. Dull aches in left arm (often with numbness, shortness of breath, sweating, post exertional) could bea cardiac symptom due to similar "wiring" between nerves going to heart and arm. These symptoms usually start centrally and radiate to the distal arm. The left leg however does not sate these nerves and a cardiac cause (like reduced oxygenation of heart due to blockages should not involve the leg.