We tested the hypothesis that cardiac myocytes from hypertensive (one kidney, one clip; 1K,1C) cardiac-hypertrophied rabbits require higher guanosine 3',5'-cyclic monophosphate (cGMP) to similarly lower O₂ consumption than control myocytes and that this effect is caused by differences in guanylate cyclase activity. Using isolated myocytes from control and 1K,1C New Zealand White rabbits, we obtained O₂ consumption (nl O₂ · min¹ · 10⁵ cells) and cGMP (fmol/10⁵ cells) levels after stimulation of guanylate cyclase with nitroprusside, CO, or guanylin (10⁸-10⁵ M). Soluble guanylate cyclase activity was also determined. Basal cGMP was elevated in 1K,1C vs. control (176 ± 28 vs. 85 ± 13) myocytes. cGMP increased in 1K,1C and control myocytes after stimulation with nitroprusside, CO, and guanylin. Guanylate cyclase activity in 1K,1C vs. control myocytes was not statistically different. Basal O₂ consumption in 1K,1C vs. control myocytes was comparable (307 ± 1 vs. 299 ± 22). O₂ consumption was similarly decreased when guanylate cyclase was stimulated. Control regression equations correlating cGMP and O₂ consumption were O₂ consumption = 1.46 · [cGMP] + 444.65 (r = 0.96) for CO, O₂ consumption = 0.58 · [cGMP] + 328.48 (r = 0.82) for nitroprusside, and O₂ consumption = 1.25 · [cGMP] + 389.15 (r = 0.88) for guanylin. The 1K,1C regression equations were O₂ consumption = 1.36 · [cGMP] + 537.81 (r = 0.97) for CO, O₂ consumption = 0.23 · [cGMP] + 307.30 (r = 0.88) for nitroprusside, and O₂ consumption = 1.27 · [cGMP] + 502.91 (r = 0.89) for guanylin. These data indicate that 1K,1C hypertrophic myocytes had higher cGMP than controls at every level of O₂ consumption. This effect was not caused by differences in basal or maximal guanylate cyclase activity.