With the month of February marking American Heart Month, doctors say improving cardiovascular health doesn’t require an expensive diet overhaul or strict food rules — just a few smart,  heart-healthy grocery-store swaps. “Focus on the additions,” said Tara Schmidt, lead dietitian for the Mayo Clinic Diet in Rochester, Minnesota. “I like to shift the focus more toward, ‘I’m going to eat more fish’ — that, in turn, will naturally decrease my red meat intake, for example.” Small changes can add up,