Two cardiac principles were isolated from nekombu (the basal part of the blade of a laminariaceous seaweed). Fatty acids of C₁₄, C₁₆ and C₁₈ were found to stimulate the isolated frog heart, while histamine dihydroiodate to accelerate the isolated guinea pig atrium. Histamine and iodine contents of nekombu were 501 mg/kg and 3200 mg/kg, respectively, indicating that 36% of the total iodine present in nekombu is in the salt form of histamine. It was also found that a small amount of histamine improves the taste of glutamic acid.