Refer to the serotonin data of Exercise 7.2.7. On what grounds might an objection be raised to

Question:

Refer to the serotonin data of Exercise 7.2.7. On what grounds might an objection be raised to the use of the / test on these data?
Exercise 7.2.7
Heart disease patients often experience spasms of the coronary arteries. Because biological amines may play a role in these spasms, a research team measured amine levels in coronary arteries that were obtained postmortem from patients who had died of heart disease and also from a control group of patients who had died from other causes. The accompanying table summarizes the concentration of the amine serotonin.