Abstract: Ascorbic acid has been used in treatment and prevention of hypo-or avitaminosis C as well as in many other clinical conditions including some cardiovascular diseases. The intravenous injection of large doses of Injectio acidi ascorbici (IAA) (pH=5.6) was known to be effective in the management of cardiogenic shock in Kershan disease. The present paper reports the experimental results on the effect of IAA on blood pressure, hearts, and blood vessels with a view to elucidating certain mechanisms of its efficacy in cardiogenic shock. In urethan-or Na-pentobarbital-anaesthetized dogs, rabbits, and cats, an intravenous injection of IAA at the dosage of 0.2, 0.4 g/kg moderately and temporarily raised the arterial blood pressure to the extent of about 10—20 mm Hg, lasting about 5—10 minutes. No significant change in heart rate was observed, but during the early phase of the elevation of blood pressure the respiration became quickened and deepened. As the blood pressure of animals was reduced below 80 mm Hg by operation and haemorrhage or various hypotensive drugs (chlorpromazine, sodium nitrite, histamine, papaverine), the pressor effect was more pronounced and sustained than that in anaesthetized animals. Solutio acidi ascorbic (SAA) always produced a drop of blood pressure, but after being neutralized with sodium bicarbonate to pH=5.6, it could exert the same pressor effect as IAA. It seemed, therefore, that the pressor effect of IAA was due to the partially neutralized ascorbic acid in it. Cardiac output, was estimated on Fick's principle in urethan-anaesthetized dogs, an intravenous injection of IAA 0.2 g/kg increased the cardiac output, cardiac index, stroke volume, and aortic mean pressure, especially in hypotensive animals. The total peripheral resistance was not obviously altered. In using IAA (1:500, 1:1000), both the contractile amplitude of Cushny's rabbit's heart in situ and of isolated rabbit's heart were enlarged; at the same time, heart rate and coronary flow of the latter were also increased. In perfused isolated rabbit's ears, hind legs, and kidneys, IAA (1:500, 1:1000) showed no remarkable effect, except a slight dilatation. During the rise of blood pressure after IAA administration, the blood flow of hind leg and kidney by Kaverina's method was increased. IAA slightly increased the spleen volume of anaesthetized dogs, while SAA always diminished it. From these results, the pressor effect of IAA seemed to be chiefly due to the improvement of cardiac function, resulting in an increase of cardiac output. It was considered that IAA might serve as an effective drug in combating cardiogenic shocks other than those in Kershan disease.