MSF does sometimes have hands-on work in emergency situations. However, most countries that hire American/British/etc nurses to go to developing countries do want administrators and educators rather than hands-on nurses, and for good reason: they have their own nurses to do the hands-on work, as it should be! That is a more sustainable model, and the nurses have the language and cultural competence to work well with their own people--not to mention that it provides them with jobs.
1.5 years in the US is barely long enough to be an independently capable nurse in the US, in my opinion (notice how many travel nurse places will only accept nurses with two years of experience), much less to deal with the challenges of nursing in the developing world or to teach nurses there. I think the three years required by MSF should be the minimum length of time you'd consider, to be honest.
My suggestion is to keep your ears open for opportunities or ideas, keep gaining experience in the US, and start studying French or Arabic. Go on short-term missions now if you like. Cardiac med-surg is fine experience, but you could also consider switching to OB, OR, or ER--specialties that are much in demand. (OR nurses are some of the few who generally keep doing the same job when they go abroad, rather than switching to management/teaching, though hopefully that is changing. But in short-term situations, experienced OR nurses from the developed world are the practical option.)
Also, it doesn't pay anything--in fact, nurses have to pay a fee to work--but Mercy Ships has nurses doing nursing work in a US-type setting, but with patients from Africa, on the coast of various countries (I think they're in Madagascar right now). Those positions range from a couple of months to many months. If what you really want to do is hands-on work with African people, it might be worthwhile to save up and take a long sabbatical from paid hospital work in the US.