Cardiac frequency and blood pressure were measured during voluntary diving in the bullfrog, Lithobates catesbeianus, exposed to 15¢XC or, alternatively, 25¢XC. Diving caused bradycardia and reduction of blood pressure. Cardiac frequency was 27.1 �b 2.2 for breath periods and 19.3 �b 2.7 for diving periods at 15¢XC, and 47.7 �b 4.4 and 35.3 �b 3.6 for 25¢XC. Systolic blood pressure was 39,6 �b 0,9 for breath periods and 36,2 �b 0,4 for diving periods at 15¢XC, and 42,4 �b 1,0 and 39,8 �b 0,5 at 25¢XC. Diastolic blood pressure was 32,3 �b 0,6 for breath periods and 29,5 �b 0,5 for diving periods at 15¢XC, and 35,3 �b 0,9 and 33,2 �b 0,6 at 25¢XC. The animal was artificially ventilated during diving with normoxic, hypoxic (5% O2) and hypercarbic gas mixtures (6% CO2). None of these procedures produced any change of blood pressure or cardiac frequency. Cardio-vascular effects have, however, been reported in some other studies on amphibians. As a new aspect, we applied artificial ventilation during a voluntary dive in the frog. Surfacing, elicited tachycardia and elevated blood pressure, These cardiovascular reflexes depend on a stimulus that still needs to be identified.