Should I ask for more tests?

I'm 21 and recently went to see a doctor because I wanted to know why my heart sounded arrhythmic in my head – I first noticed it when I was 14, but my doctor said it was nothing to worry about. This time I was sent to see a cardiologist. They did a Holter test  (sinusrhythm tends to be tachycardic, no pauses. Rare supraventricular and ventricular extrasystoles) and then a cardiac stress test (resting ECG: tachycardic, functional capacity: 8.7MET, HR response to exercise: hyperkinetic, BP response to exercise: normal, no chest pain, no arrhythmias, no ST changes) , ten minutes later I was diagnosed with "Cardiomyopathy in infectious and parasitic diseases classified elsewhere (I43.0)" accompanied by "other specified heart irregularity" and "supraventricular and ventricular extrasystoles" and "fits of tachycardia" (I49.8) although I wasn’t ill as a child. The doctor told me I might have had a hidden tonsillitis and prescribed me Metoprolol. I was told not to gain weight, to be careful with exercise and do a stress test once a year; then I was sent back to my family doctor who decided to check my blood for anemia - I'm currently waiting for the results.
I don’t have many symptoms, but I have trouble falling asleep because my heartbeat doesn’t slow down enough and I’ve never been able to run without becoming lightheaded, but I’ve never been very athletic either. I do enjoy walking and a 30 mile hiking trip isn’t a problem.
What I really don't understand is where I43.0 falls on the list of cardiomyopathy types. Is it dilated or something else? Is I43.0 a completely different type? Is my heart muscle damaged and will I be on medication for the rest of my life?
Should I go to another cardiologist to get a second opinion and ask for some more tests?
*I'm 11lbs overweight and my family has a high risk of hypertension (usually becomes a problem after we gain weight, which is another thing we are prone to). My glucose, cholesterol and magnesium levels are normal.
Thank you!

[CCFCardio MD2]

I wouldn't pay much attention to the I43.0 code.  It is just a billing code for cardiomyopathies not otherwise specified.  It isn't a specific diagnosis.  I'm not sure you have a cardiomyopathy (weakened heart).  I haven't heard anything in your post that indicates that.  The tachycardia and lightheadedness with exercise is slightly concerning, but it sounds as if your doctor is following.  If you aren't satisfied with the answers you're getting you could always try another cardiologist for a second opinion.  Watch your weight, eat well, and follow closely with your physician.  

Best of luck.

[mvg918]

You should watch your blood pressure closely to make sure it isn't elvated greater pressure (resistence) can make your heart bigger.  My sister had high blood pressure and got a log to keep record of her blood pressure over months, It really helped her to keep a real idea of her BP.  she got it from ****************.net I thnk amazon has blood pressure logs as well.