Are you up to dealing with intake procedures in Spanish in the clinics? I am fairly certain that the vast majority of the cardiologists in the major clinics like Favoloro, Fleni, Hospital Italiano, ICBA, would speak very good English. In ICBA, which I can totally recommend, various consultants spoke English with me with no prompting.
One problem with an independent cardiologist is likely to be a lack of equipment.
ICBA organize international conferences, and, until recently, were a destination for medical tourism. You would not go wrong with them.
Your problem is likely to be less with the cardiologists and consultants, and more with the secretaries and people who need to compile your data and arrange your appointments. No matter which route you go, you will probably have to deal with this.