Abstract 1. 1. Diltiazem at doses of 2.5, 25, and 50 mg kg caused a reduction of minute ventilation of hamsters over a 60 min period compared to saline administration. 2. 2. The decrease of ventilation was due to a fall in frequency of breathing, but predominantly due to a decrease of tidal volume. 3. 3. The pattern of metabolic response of hamsters to diltiazem was different to the ventilatory response—but metabolic rate was decreased in all animals receiving diltiazem by 60 min compared to pregavage values.