The Circulation study employed observational data, but its initial aim was not to assess the relationship between coffee and heart failure. This is how the lead author David Kao, a cardiologist at University of Colorado School of Medicine, characterized it to me: “The overall question was, What are the factors in daily life that impact heart health that we don’t know about that could potentially be changed to lower risk.” Because one in five Americans will develop heart failure, even small changes in their behaviors could have a big cumulative impact.