A series of 1-methyl-7-(4-pyridyl)-5,6,7,8-tetrahydro-3(2H)-isoquinolinones and relatedcompounds were synthesized and evaluated for positive inotropic activity. Most members of this series exerted a dose-dependent increase in myocardial contractility in the dog acute heart failure model, whereas they caused only slight changes in heart rate and blood pressure. Several derivatives, especially those