Cardioactive drugs--beta-adrenoblocking agents (propranolol, trasicor and cordanum) and Ca2(+)-antagonists (nifedipine and phenoptine)--exhibited both activating and inhibitory effects on proteolytic activity in rat heart tissue extract. The beta-adrenoblocking agents did not affect distinctly the activity of partially purified cathepsin D and Ca2(+)-dependent neutral protease from myocardium. Nifedipine inhibited cathepsin D by 50% and Ca2(+-dependent neutral protease--by 75%; phenoptine inhibited also the latter enzyme by 30%.