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1 Heart rate and blood pressure changes following the administration of alinidine 30 mg alone and in combination with atenolol 25 mg, nifedipine retard 20 mg and glyceryl trinitrate 500 ,ug were investigated in three groups of six healthy male volunteers. 2 Concomitant administration of alinidine and atenolol reduced (P < 0.05) supine, standing and exercise heart rate when compared with alinidine alone. The maximum reduction in exercise heart rate was 116 ± 2.4 beats min-1 for the combination vs 129.0 + 3.1 beats min-' for alinidine alone.3 Supine (3, 4, 8 h) and standing (2 h) systolic BP were also reduced (P < 0.05) with the alinidine and atenolol combination compared with alinidine alone. Little change occurred in diastolic blood pressure. 4 Alinidine and nifedipine in combination reduced (P < 0.05) the nifedipine induced increase in heart rate in the supine (2, 4 h) and standing (4 h) position and following exercise (2, 4 h). No further decreases in systolic and diastolic blood pressure occurred with the combination. 5 Alinidine administered 2 h before a glyceryl trinitrate challenge reduced (P < 0.05) the glyceryl trinitrate induced increase in standing heart rate at all time intervals (1 to 6 min); the maximum reduction occurred at 3 min (105.0 ± 4.3 (glyceryl trinitrate) vs 86.8 ± 6.7 beats min-' (combination)). Systolic blood pressure was further reduced at all time intervals with glyceryl trinitrate taken in the presence of alinidine. 6 In conclusion alinidine potentiated the heart rate reduction of atenolol and reduced the reflex increase in heart rate associated with nifedipine and glyceryl trinitrate. The combinations were well tolerated except in the case of alindine and glyceryl trinitrate where four out of six subjects felt light-headed.