Myocardial Infarction: Metoprolol tartrate is contraindicated in patients with a heart rate <45 beats/min; second- and third-degree heart block; significant first-degree heart block (P-R interval ≥0.24 sec); systolic blood pressure <100 mmHg; or moderate-to-severe cardiac failure (see Warnings), known hypersensitivity to metoprolol and related derivatives.