Then or = (40/60)/(20/80) = 40 * 80/20 * 60 = 2.67. Its significance can be basically equivalent to: the risk of myocardial infarction in hypertensive people is 2.67 times that in non-hypertensive people.
The risk factors and protective factors that often appear in that paper will be compared with 1 when the researchers get the OR value through statistics. If the OR value of a factor is greater than 1, then this factor is the risk factor of the disease; That is, people who carry this factor have a high risk of illness. If the OR value is less than 1, then this factor is the protective factor of the disease; People with this factor have a low risk of illness.
We assume that if hypertension has nothing to do with myocardial infarction, then it can be inferred that the incidence of myocardial infarction is the same in hypertensive people and non-hypertensive people. In other words, the incidence of myocardial infarction in people with hypertension = people without hypertension. Because the case-control study can't get the incidence, we have to infer that the hypertension/hypertension ratio of myocardial infarction cases is the same as that of non-myocardial infarction control groups. When the above hypothesis holds, OR= (hypertension/hypertension ratio in myocardial infarction cases)/(hypertension/hypertension ratio in non-myocardial infarction control group) = 1. From what I said above, you should understand why our OR value should be compared with 1.