I was diagnosed with supraventricular tachycardia about 2 years ago and take Cardizem. Recently I've noticed an increase in feeling short of breath on exertion and I've developed some phlegm in my throat like you might have with allergies, although I'm really not coughing. I cough once in a while, but I can't tell if the phlegm is coming from my chest or maybe my sinuses. I had a normal chest x-ray about a month ago and my doctor says my lung sound okay, but I'm wondering if I could be developing congestive heart failure. Has anyone else had these symtpoms with a different diagnosis? I'm only 41 years old, but I smoked in the past, although I no longer smoke, and I am obese.