Abstract: An isoquinoline derivative represented by the formula (I) ##STR1## wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5 and A are as defined in the disclosure, or a pharmacologically acceptable acid salt thereof. These compounds have an excellent relaxation action on blood vessels, particularly coronary arteries, and on bronchial tubes. Accordingly, the compounds can be advantageously utilized as drugs for prevention and treatment of angina, myocardial infarction, cardiovascular thrombosis, cerebrovascular thrombosis, hypertonia, asthma and other various circulatory and respiratory organ diseases.