The action of nitroglycerine and dipyridamole in normal and ischaemic dog heart.

1 Network and post-network resistances were measured together with heat clearance and heat production in the myocardium. 2 Nitroglycerine dilated all resistance vessels but was twice as effective on network as compared with post-network vessels. 3 Dipyridamole dilated network and post-network vessels equally. 4 Nitroglycerine had no effect on heat clearance or heat production in ischaemic myocardium. 5 Dipyridamole increased heat clearance in normal but not in ischaemic myocardium. 6 Dipyridamole depressed heat production in normal and ischaemic myocardium. 7 That the clinical effectiveness of nitroglycerine does not depend entirely on its coronary vasodilator properties is confirmed. 8 It is suggested that the action of dipyridamole in depressing myocardial heat production may be due to an action on the efficiency of oxygen utilization during cardiac contraction.