Step 1: MONICA is a well-known WHO acronym in cardiovascular epidemiology.
Step 2: It stands for Multinational MONItoring of trends and determinants in CArdiovascular disease, which is where the letters of the name come from.
Step 3: The project ran across 41 centres in 26 countries over a 10-year period ending in 1994, studying why coronary heart disease and stroke trends differed between populations and how risk factors, treatment and case-fatality contributed.
So the correct expansion is cardiovascular disease.
Ref: Park Textbook of Preventive and Social Medicine, 24e, p.385.