There can be shortness of breath without heart problem, but because of the seriousness of the symptom you should see a doctor as soon as possible to rule out a heart disorder. I was admitted to ER for the symptom of SOB. I was told by the intake personnel shortness of breath is all that is necessary to be admitted. I was shocked to hear after preliminary tests that I had had a heart attack...no chest pains, etc.
Arteries can be clear, but your cardiac output can be reduced and that would be consistent with a low CO. An echocardiogram would be appropriate to rule out any hypercardiomyopahty (enlarged heart) and any valve insufficiency, etc.