Hello, It appears you probably have Angina pectoris, which does the symptoms as described. There may not any tell tale signs. It may get precipitated due exertion. The reason for angina is coronary arteries tend to develop plaques due to fat deposits, blocking or reducing the blood supply to the heart muscle. This condition can be relieved by Glycerile nitrate, which dilates the coronaries, restores blood supply. ECG may not show any changes. Aspirin is given to maintain proper flow of blood, by preventing adherance of platelets. It will further investigations like echocardiogram and angieography, to see what is the extent of block is present in the coronaries. Plus you will have to avoid high fat diet, smoking and even alcohol. So it better if you consult a cardiologist and go through other investigations based on his opinion. Thanks.