L-arginine increases the risk of heart attack only in people who have already had heart attacks, states MedlinePlus. However, this amino acid has many possible side effects, including abdominal pain, bloating, diarrhea, blood abnormalities and low blood pressure. Allergic reactions, airway inflammation, gout and asthma sometimes occur as well.
In addition to heart attack victims, other people should use caution when considering using L-arginine, according to Medline Plus. Patients with kidney disease should avoid it, because it sometimes causes deadly complications. High doses are potentially fatal to children. L-arginine worsens certain conditions, including asthma, allergies and low blood pressure. Pregnant and nursing women should avoid it because the long-term effects on the fetus and on babies are unknown.