hi, thank you for providing a brief history. well as you mentioned in your message about you feeling uncomfortable on left arm and hands. well ofcourse one will get panic and look for a cardiac symptom. it is really to appreciate that you took immediate step and met a cardio. now since the cardio has mentioned about not to worry with the anything as nothing is wrong let s look up to the other factors. it may be a stress or work related issue. Since you mentioned you do a lot of typing that means you use a computer and there will be a lot of stress on the muscles around the neck and the chest muscles. now taking this into consideration about your job profile I suspect it to be a issue with your repetitive stress injury. that means you have pain and aches due to work related issues. constant sitting, long hours working, position of your neck and arms. why don t you try doing some regular breathing exercises, meditation, simple neck exercises and upper limb exercises. kindly see to even this that you take regular frequent breaks during your working time. as it will help to avoid stress on muscles and avoid work related injuries. hope you will be fine.