Just to clarify for you where your statement was going wrong:
WHERE physician_spec = ('Cardiology' OR 'Invasive Cardiology' OR 'Noninvasive and Invasive Cardiology')
i believe this gets intepreted as WHERE physician_spec = (TRUE).
What you ought to have had would have been :
WHERE (physician_spec = 'Cardiology') OR (physician_spec = 'Invasive Cardiology') OR (physician_spec = 'Noninvasive and Invasive Cardiology')
However, the "IN" answer that has been provided by Rudy is the best...