A cardiology fellowship typically takes three years to complete after initial training in internal medicine. This is followed by further specialized training if one wishes to pursue sub-specialties like interventional cardiology, electrophysiology, or advanced heart failure and transplant cardiology, which typically require an additional 1-2 years. So, overall, after completing medical school and internal medicine residency, you’re looking at 3–5 years of additional training to become a fully trained cardiologist with a sub-specialty.