Mexiletine is a type I antiarrhythmic drug that is structurally similar to lidocaine. Mexiletine has considerable potential for causing neurologic, cardiac, or gastrointestinal side effects. However, mexiletine does not undergo clinically significant first-pass metabolism and, thus, has good oral bioavailability. Mexiletine has a large and variable volume of distribution and an elimination half-life ranging from 6 to 12 hours. Mexiletine disposition is probably altered in patients with heart failure, liver disease, and severe renal dysfunction. Efficacy and toxicity are not well correlated with mexiletine serum concentrations. Mexiletine is as effective as traditional antiarrhythmics in the treatment of premature ventricular contractions. However, in patients with drug-refractory inducible ventricular tachycardia, mexiletine is usually ineffective when used alone. When mexiletine is combined with other antiarrhythmic agents, a significantly higher percentage of patients with this difficult arrhythmia have a good response. Mexiletine is a potentially important addition to the existing antiarrhythmic drugs currently available, but its place in the clinical setting and in therapeutic drug monitoring is not well defined at this time.