Cardiology is a MINIMUM of 3 years following 3 years of IM. About half the programs in this country are 3 yrs. for general Cards, and half are 4 years (1 yr. research). General Cards includes diagnostic cath training. Subspecialties within Cards (=further years of training) include:
Interventional Cards: 1-2 years depending on the program and depending on how much peripheral intervention you do
EP: The AICD/pacemaker/ablation guys. Generally 1-2 years after general Cards, but many places let you fold in your first year of EP into your last year of general Cards fellowship
Heart Failure: Generally 1 year more after general cards
ECHO: 1 year, including more TEE training.
Preventive: 1 year, from what I understand
Int. Cards and EP are by far the most procedure intensive.