“ Isosorbide dinitrate (5 mgm sublingually) while sitting unloads both … (p < 0.01) and the mean R —R interval (p < 0.005), increased the power of the low-frequency (LF) component of the R—… high-frequency (HF) component (p < 0.005) and increased the LF/HF ratio (p < 0.05).”