I can't possibly think of how a hypertension fellowship by itself will make you more competitive. PCP, FM, IM, chiropractors, dieticians, nephrology, obgyn, treats HTN. If i was trying to be competetive in cardiology, id find some research work and something more productive. Doubt just having a htn fellowship on yr cv is worth much, unless you have no other option and want to do something clinical that year.