“Single … nifedipine (0.3–10 μg), verapamil (1–30 μg), diltiazem (…–300 μg), lidocaine (100 μg–1 mg) and procaine (300 μg–3 mg) produced a dose-related increase in the A-V conduction time … of these drugs a second or third degree block of A-V conduction occurred.”