The differences in the pattern of the vasoactive hormone release in response to the stress of surgery and cardiopulmonary bypass (CPB) (pulsatile n = 15 and non pulsatile n = 23) were studied in the adult patients with mitral valve disease (MVD), aortic valve disease (AVD), and the coronary artery disease (CAD). A differential stimulation of the osmoreceptors, baroceptors, renin-angiotensin and the sympathetico-adrenal systems in these patients, resulted in the variations in the pattern of hormone release. Patients with MVD showed a greater stimulation of osmoreceptors, baroceptors and release of Arginine vasopressin (AVP). Renin-angiotensin system was more easily triggered in patients with AVD or CAD; and sympathetico-adrenal system in patients with CAD. The renin-angiotensin-aldosterone axis was better preserved in patients with CAD (r = 0.49, p less than 0.001) than in the patients with MVD (r = 0.38, p less than 0.02). Plasma renin release showed a significant correlation with noradrenaline release in the patients with MVD (r = 0.47, p less than 0.01); but this relationship was lost in the patients with the CAD, due to an excessive noradrenaline release. Pulsatile bypass reduced but did not abolish this response. Under unfavourable conditions, the stress response may persist in the early post-operative period.